I can't help noticing that some of these meetings were when the celeb was on duty (signing, official meets, performing etc) whereas others were spotted in the street, met whilst fm was at work, whatever.
Perhaps some of those who seemed nice in the former circs might be absolute horrors if met in the second. You'd have to be an idiot not to put on a smiling face when scheduled to meet your fans.
The horrors always come across as the most interesting in my opinion. Although I suppose I mightn't feel that way if I was the one doing the meeting.....
I haven't met anyone famous myself.