Steven Seagal. Sorry, Shia Lebouf, Nic Cage and even Schwartzniger have should at least some sort of talent for acting and had a least on good notable role that showed an understanding of drama.
Seagal has never shown any of this, he can't act and he can barely bloody fight (most of his movies now he has mostly stand-ins for most fight scenes). He's got all the emotion of a brick wall, if the brick wall was a fat, over bloated, sexist, racist, ego driven prick.
Hell even JCVD showed that he can act in at least one film (Look up JCVD), Statham has Lock Stock and Snatch, Sly Stallone has Rocky, First Blood and Copland... Seagal? Nothing...
As for female actresses. Catherine Heig. She did well in Knocked up then denounced the movie (she didn't get the character and thought it was sexist) then released and starred in her own movies where she has all the emotion as Steven Seagal only with added pretension.
Not sure how fair it is to hate on actors for playing themselves. Long as they do it well then what's the problem? Also, I've seen Hayden Christian pop up a few times. I don't really think that's fair. The most well known movie he was in was the prequel series that wasn't all that well written, the films had Liam Nielson, Ewan McGregor, Sam Jackson and Natalie Portman and even they could pull it off and make that movie any good. So I don't think it's fair to rule out Hayden on that one.