Most career walks, most HR in a season, most HR in a career...
Barry Bonds
Most steroids ever used. Barry Bonds
As Barry Bonds approached his record-breaking home run, many in the audience were holding up signs featuring a giant asterisk.
Lousy cheat
I went to game a where the Giants played the Marlins. Marlins manager Jack McKeon intentionally walked Bonds on his first three at bats...with nobody on base! After the game he was unapologetic, saying he wasn't going to let Bonds have any chance to beat him.
If I recall, the Giants did lose. :)