2. Adam Sandler
In the nineties, Adam could do no wrong; he starred in Happy Gilmore, Big Daddy, The Wedding Singer, The Waterboy and Billy Madison. He was friends with Chris Farley and cast his best friends in his movies. He made date movies that weren't date movies and most important, his characters were ones we felt we could identify with in some way.
What so happened? He broke up with Tim Herlihy; his ex-college roommate and writing partner that helped pen all the above movies. Without him, Sandler has basically shit out turd after turd since early 2000, living the actor's life of multiple personalities. He drifts between roles that are all glimmers of parts seen in his earlier movies. It's like he is unable to decide if he wants to be 'angry funny' like in Anger Management, or the 'sad funny' like in Punchline or the 'rom-com guy' like in 50 First Dates. He also ventured into Dramatic Robin Williams leading man territory with Reign Over Me which looks to be the same movie as William's The Fisher King. His most recent turds, Jack and Jill and That's My Boy seem targeted mainly towards 13 year old boys with parent issues.