22 years ago, the Houston Astros gave their first base job to rookie Jeff Bagwell, after acquiring him from Boston six months prior. He went on to win Rookie of the Year that season. Three years later, he was the NL MVP.
Bagwell remained a Houston Astro thru 2006 (although disabled most of '05 and all of '06.) During that time, he turned stomach-punching the Giants into his personal project. When he makes the Hall of Fame, every Giants pitcher from John Burkett on through Russ Ortiz deserve mention in his speech—without them, he's a rich man's Travis Lee.

Okay, that's hyperbole. But Bagwell sure did feast heartily on Giants pitching.
Bagwell slugged .640 against the Giants—far more than any other NL team.
Bagwell batted .348 against the Giants—far more than any other NL team.
Bagwell took Giant pitchers deep 32 times—among NL teams outside his division (Central), only the Padres were victimized more (35).

Before Jeff Bagwell entered the major leagues, Roger Craig had long, curly black hair and Livan Hernandez weighed 180 lbs—stress from going up against the Astro superstar changed all that!
Since his forced retirement, no one has quite supplanted him as a year-in, year-out Giants killer.

St. Louis outfielder Matt Holliday is more of a Giants villain. Arizona first sacker Paul Goldschmidt seems more than capable of the role—but most of his damage so far has come versus one man, Tim Lincecum. If Lincecum leaves SF as a free agent this winter and Goldschmidt maintains healthy production against the Giants, he may become the Bagwell of the 2010's.

Until then...
This blog highlights the top nemeses of the 2013 Giants (batters only). While all these players have good numbers against the Orange and Black this year, good numbers don't necessarily guarantee a player's inclusion. Many factors went into my selections, too many to list. One standout game (a la B.J. Upton, Justin Ruggiano or Yuniesky Betancourt) won't warrant mention.

Carl Crawford
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Crawford, the longtime Tampa Bay Rays star, had become the most irrelevant $160 million man in U.S. history by the end of 2012. Expected to anchor left field at Fenway Park for the rest of the '10s after being signed by the Red Sox, he only lasted a year-plus before undergoing elbow surgery and having his contract dumped on the Dodgers.
He proved he was healthy and ready to produce on Opening Day '13, going 2-for-4 (with a caught-stealing, however) in the Dodgers' shutout of San Francisco April 1.
April 3: in a 5-3 Dodger loss, he singled three times, drew a (questionable) walk, and was robbed of a fourth hit by a Brandon Crawford barehand.
In between, Carl Crawford pinch-hit a popup high enough to scrape the roof of his old home park, Tropicana Field, had he hit it there (it was caught).

May 3: Crawford pinch-hits an infield single to extend a Dodger rally that was soon snuffed out in a 2-1 loss.
May 4: Crawford singles twice, beats out a double-play ball and scores, steals a bag, and drives in the go-ahead Dodger run via fielder's choice, but the Dodgers lose 10-9 on a Buster Posey walk-off.
Through June 23, The Dodgers are only 1-5 against the Giants this year—but their resurgent left fielder is not to blame. (Note: Crawford is on the DL with a hamstring injury and is expected to miss the entire June 24-26 SF/LA series.)

Eric Chavez
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A potentially great career derailed by four years of injuries, Eric Chavez isn't the same player who annually put up 30 homers/100 RBI for the Oakland A's—unless he's facing Giants pitching in the year 2013. 

He ripped an impressive oppo homer against Ryan Vogelsong on April 22. The next day he singled and walked in a D'back victory over SF. When the Snakes came to San Francisco April 29, Chavez beat out an infield single and smacked another home run (this one off Matt Cain).
After a day of rest, the veteran third baseman returned May 1 and registered three hits—two singles and a deep RBI double (although he was erased trying to stretch it into a triple.) Chavez missed the most recent Giants/D'backs series recovering from an oblique injury—I'm sure Bruce Bochy's team was just heartbroken.

Carlos Beltran
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If only Beltran played as well for the Giants as he did against them.
Not that the veteran outfielder's acquisition in 2011 was a bust—Joe Fan's retrospect, often skewed by bitterness over Beltran picking St. Louis over San Fran that winter, would have one believing Beltran was the second coming of Ryan Garko. But that's simply not true.
What is true: he had injuries and the team only went 25-28 after trading for him. But to blame Beltran for that, when he and Panda Sandoval were the only two reliable hitters in the Giants lineup down the stretch doesn't seem fair.

Beltran may not have been 2008 Manny Ramirez. But the guy hit .323 and slugged .551 with seven jacks in under 200 at-bats. He ripped seven straight hits at one point. He raised his season average 14 points after swapping the Orange and Blue for the Orange and Black. In just under half the at-bats, he had three fewer RBI than Aaron Rowand. He led the team in triples playing only 44 games. He threw out six runners and did not commit an error. And if he were a malignant clubhouse tumor, it was a well-kept secret—at least one report I scoured during his tenure expressed the exact opposite.

It seems Beltran, unfairly, became symbolic of the Giants' late-season fade (they were 61-48 pre-Beltran) as time wore on—the lengthy absences of Buster Posey, Freddy Sanchez, Barry Zito, Pat Burrell and Jon Sanchez not to mention year-long slumps by Rowand, Miguel Tejada, Cody Ross, Aubrey Huff, and Andres Torres being conveniently forgotten. 

So when I type that opening line, it is not a knock on Beltran's Giants stint—rather, it's a testament to his 2013 excellence versus his former teammates. 
In his first 2013 at-bat against SF, he grounded sharply into a twin killing—running to first at roughly 65 percent. (Never did get an explanation for that.) Since then...

Beltran drove in three runs the next day in a 6-3 Cards victory, then walked, scored and drove home two more before being removed in a 14-3 Cardinal blowout. In the lineup for just one of three games SF played in St. Louis, Beltran made it count—driving home two runs and scoring another in a 7-1 victory. That's seven RBI in four games.
Barring a postseason rematch, the Giants have seen the last of the scrappy 2013 Cardinals. I, for one, won't miss them.

Melky Cabrera
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A player for the Blue Jays who recently played two-thirds of a season for the Giants, Cabrera treated his former teammates very rudely when they traveled up north for a two-day stay in Toronto.
Cabrera began things by reaching on an error and scoring; he then banged out four hits in as many at-bats, driving in two runs and scoring another in a 10-6 Toronto win. The next day he doubled, walked and scored each time in an 11-3 Jays victory.

Cabrera raised his average 18 points in just those two games, making but two outs—and one of those nearly ripped through RF Hunter Pence's mitt, it was scalded so hard. 
San Francisco contained Cabrera somewhat when the Jays came west; perhaps humbled by a chilly reception from a crowd who adored him less than a year ago, he went 2-for-4 in the first game before going hitless in the finale.  

Marcell Ozuna
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Playing his first-ever career games against the Giants June 20-23, Ozuna was the primary reason his Miami Marlins took three of four from the defending World Champions. Well, that and San Fran's lamentable hitting.

In the eighth inning of the first game, Ozuna came off the bench and cracked a game-winning, two-run single in a 2-1 Miami win. In Game Two, he went 2-for-4, including game-tying and tiebreaking RBI singles as Miami won 6-3.
Contained in a 2-1 loss in the third game, Ozuna busted out big-time in the finale. He turned on a heat-seeking Matt Cain fastball and ripped it into the left field corner for Miami's second run. Later in the affair, he crunched a similar pitch from Jean Machi off the left field fair pole—the Marlins won that one 7-3.

Ozuna's series totals: 6-for-14, six RBI, .786 slugging. Any chance he could take paternity leave beginning August 16?

Carlos Gonzalez
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I remember thinking: the Rockies traded Matt Holliday and he (Gonzalez) was the primary return?
Hence the rule for not evaluating trades involving young players for at least three years.

Gonzalez immediately inherited not only Holliday's uniform number and position upon his acquisition from Oakland four winters ago, but also his status as most-feared hitter in the Colorado lineup—he's been an All-Star, batting champion, and nearly an MVP. Plus, he's a two-time Gold Glover.
This year he's leading the league in homers and runner-up in slugging (thru June 23), which Giants fans have no trouble believing. Though he's whiffed 11 times, he's also smoked three homers against San Francisco pitching, including the ultimate diss—two bombs deposited into McCovey Cove. (Am I the only one who considers that a diss? Not quite on the level of Casey Blake mocking Brian Wilson's arm cross...but close.)

Gonzalez, save for the first Cove homer, was quiet in the Rockies initial visit to AT&T Park—a Giants sweep.
A month later, Colorado took three of four from their rivals; CarGo drew seven walks, stole three bags, drove in seven runs, scored five, and banged two homers—both longballs coming in the second game. Back in SF the following week, Gonzalez ripped two more jacks (including Cove shot No. 2) as well as two singles.

And to think, the Giants have nine more clashes with the Rox this year, including three to close out June...

Honorable Mentions
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These players have also caused Giants pitchers grief, albeit in smaller doses, hence their relegation to honorable mention status:

Dioner Navarro, Cubs. The part-time catcher and former All-Star came off the bench and swatted a ninth-inning, game-tying solo home run off Sergio Romo April 12 (Chicago soon won). The next day, with the Cubs down 3-0, he ripped a two-run pinch homer off Madison Bumgarner—but the G-Men held on.
Navarro received the start in the rubber match, but was quiet save for an intentional walk—although he nearly clobbered Romo with a line drive in the 10th.

Cliff Pennington, Diamondbacks. Never known for his bat, the strong-armed middle infielder has seemed to square up every pitch the Giants have thrown him, though his overall numbers don't stand out. 
On April 22, he ripped a late double in a close game that fortunately didn't hurt the Giants. One week later, he doubled and started a (failed) ninth-inning rally with a single. After going 1-for-3 in a one-run D-Back loss, Pennington took Lincecum deep with two men on and later ripped a full-count RBI double off Javier Lopez in a seesaw affair ultimately won by the Giants.

Suddenly faced with a surplus of middle infielders, Kirk Gibson only played Pennington in the finale of the most recent SF/ARI series in early June; he singled and drew another intentional walk. It should also be noted the ex-Athletic has been, pound-for-pound, among the Giants' toughest outs in the '13 campaign.

Brian McCann, Braves. In May, Atlanta visited San Francisco—and the perennial All-Star quickly made himself at home. He ripped three hits, including a homer, and drove in three runs in Atlanta's 6-3 opening win. He crunched another two-run jack the next night and also drilled one off the body of Matt Cain, who recovered for the 1-3 putout. After a day off, he drew two walks and reached on an error in the finale, a Brave loss.
Relatively quiet when his team hosted the Giants in June, McCann started all three games, managing two hits in the second and two walks in the third.

Ed Lucas, Marlins. This 31-year-old rookie seemed to be in the middle of every Marlin rally in their four-gamer at AT&T Park in June. Matching Ozuna's output, Lucas went 6-for-14 and cracked his first MLB home run off a Barry Zito curveball. He scored four times and raised his season average 20 points.