William Shatner, Beyond cretinous and spoilt. So far up himself he can tickle his own tonsils. Seems to be getting worse as he gets older.
I've heard many tales of William Shanter and what a git he is. So much so that I really don't want to meet him if I ever got the chance. He's an absolutely awful convention guest by most accounts, to the point where people call any bad convention experiences with a guest a "Shanter experience" on one convention forum I lurk on.