I met Al after a show once and he was perfectly cool and pleasant, even though he was understandably beat. I complimented the Blackhawks jersey he was wearing, so that might have warmed him up (this was during the team's dark years too). Thrill Kill Kult opened for them and they were all great.
Pretty much every interaction I've had with celebrities has been alright. Only weird one was Mira Sorvino. She was really friendly, but was insistent that she came up with the idea's for Pan's Labyrinth and Inglorious Basterds. I can't remember what she said about Basterds, but she claimed that she had a journal that she lent Guillermo del Toro during Mimic that had the basic ideas that eventually became Pan's.
Jim Jarmusch is a saint. Also, really self-deprecating about his own movies.