For me it's definitely Ritchie Blackmore. One of the greatest guitar players of all time but I'd rather enjoy him from a distance because he's also a legendary asshole.
This gal that works at Ralph's Supermarket by me used to work at the one in Malibu. I asked her if she ever dealt with Nick Nolte and Mel Gibson and if they were assholes. She said she saw them there but they were fine but the biggest, rudest, pain in the ass diva was Tom Hanks. She couldn't stand him.