He likes to do voices. In "Kickass" he does a second-rate Batman (ala the '60s TV show with Adam West). Aparently nobody on the set knew he was going to do that, and it took everybody by surprise. People thought he had gone mental until the director clued in.

What goes around, comes around. When he appeared in Peggy Sue Got Married, one of his breakout roles, he modeled the voice of his character on cartoon character Gumby, going against the wishes of the director (his uncle) and writers (my brother), costing millions of dollars from the movie's profit. He was a jerk back then, and still is, apparently.