Thank Zach Galifianakis for this one. Earlier this week he was quoted as saying:
"A movie you're acting in, you don't have a lot of control; you just show up and vomit your lines out. I'm not the boss. I'm in deep protest right now about a movie I'm working on, up in arms about something. But I can't get the guys to [listen]. ... I'm not making any leeway."
The allusion was widely believed to be about Gibson's cameo in Hangover 2. Gibson was canned shortly thereafter. Director Todd Phillips had this to say:
"I thought Mel would have been great in the movie and I had the full backing of Jeff Robinov and his team. But I realize filmmaking is a collaborative effort, and this decision ultimately did not have the full support of my entire cast and crew."
Good on Zach and company for protesting. Sad face for Todd Phillips and whomever thought the choice of Gibson was a good idea.