One of my friends was a fan of the Cure and was delighted to bump into Robert Smith, saying he was a fan, to which Smith replied, " no you're not" in some weird drone. What a stupid remark to make.
My brother met Dave Pearce, Radio 1 DJ, in Majorca and found him pleasant enough and totally not up himself.
A friend of my Uncle's met Robert Smith and said he was pretty rude, but then I've heard other people say different. Maybe it depends what mood he is in when you catch him