Coolest are usually the 'C' & 'A' listers. B-listers seem to be shitty because they think they should be on the A-list. Denise Crosby from Trek, Peter Capaldi, & Karen Gillan were some of my career favorites. Gillan had a problem question from a guy I had to gently dismiss.
Cringiest shit usually comes from people who are slightly touched in the head and the thing is I don't want to just kick them off the mic as much as try to diffuse the situation. The Gillan guy asked a canon question and couldn't understand why Gillan didn't give him an answer when we both explained that actors aren't in the writers room and don't know these things.
The common problem questions are about shipping, 'requests' (Can I get a hug? Can you sing Happy Birthday?) people who give rambling speeches before their question, and people ask the same question somebody else did. Mind you I ask people NOT to do all that stuff at the beginning.
It also kills me when we have a line of 20+ people, 5 minutes left and still folks will get in line thinking we'll get to them.