Mel Gibson has a reputation for being a lot of things, but practical joker is one that he would at least happily admit to. On more than one occasion, Gibson reportedly gifted women he worked with freeze-dried rats (including Julia Roberts), which apparently has something to do with the fact that he gets a kick out of making girls scream. “He has this thing on a set where he has to impress someone, as if he was an unattractive 12-year-old-boy,” G…