While I certainly can concede on no-brainers like Pauly Shore, my latest pet peeve in this vein has to be Will Smith. Every time I see an I Robot trailer, a part of my childhood dies. Since the ad runs so much, I'm now having trouble remembering ferrying those big dusty Asimov tomes from the library, eagerly cracking the plastic coated dustcovers to lose myself in the worlds contained within. Replacing my fond memories are images of Will dialing in the same smack-talkin' Big Willie character, tearing up the scenery to the accompaniment of overblown pyrotechnics.
Will always ruins a movie for me because to me, he is That Guy In the Back of the Theatre. You know the one- The guy who bellows throughout the movie, shouting out his idea of clever rejoinders. Normally by watching the movie on DVD, you can avoid That Guy... But when Will Smith helms a movie, you can't escape him, because he's now the grinning-ear-to-ear protagonist. He's a definite deal-breaker for me. As a rapper, he was always soft. As an actor, he's positively talcum.
As for others, here's a brief stream-of-consciousness 2AM list:
Lorenzo Lamas, Steven Seagal, although watching him die in Executive Decision made the movie, Melanie Griffith, Jeremy Irons, which is a sad state of affairs, *not* John Malkovich, although he almost made the list after seeing him in Rounders and Knockaround Guys back to back, but as long as he avoids accents he's fine, Jennifer Tilly, probably for the same reason as Melanie, the baby-voice falsetto whisper, Dana Carvey, who seems hellbent on making us forget he was ever funny, Andy Dick, who never was, David Spade, who now only illustrates how much he owed to Farley, and... that's where the stream runs dry enough that I don't feel like dredging the depths any longer.