I see what you mean. I would actually not approach a celeb if I saw them going down the road or trying to do their shopping, or all that sort of normal stuff. They are "off duty" then and owe nothing to anyone, and, I think that should be remembered and respected.
Of course, nothing is foolproof. I've read of plently of people who have had bad experiences at organized conventions and premieres so just because it's an organized event that doesn't mean you shouldn't be prepared for anything.
Celebs are real people who have good and bad days and, like real people, some are nice and some are not. You just have to go with it and if you have a bad experience, it's a shame, but it's how people can be - all people.
I was in an Italian restaurant with Ken Kercheval last year and people kept approaching him while he was trying to eat. He was very gracious and signed stuff but I thought it was rude the people couldn't wait until he had finished.
I forgot a couple on my list earlier:
Kaye Adams - Lovely woman. We had drinks and she was funny and interesting
Daniel Faison (The black guy in Scrubs) - really nice guy. Met him while bowling in LA. I was chatting to him with no clue of who he was until my rather starstruck daughter told me. He happily had a picture with the kids
And just to elaborate on the people I mentioned earlier:
Lorna Luft Initially met her as a fan but we have become good friends
Ken Kercheval - met through Lorna when they appeared in theatre together
Lorraine Chase - Again met through Lorna
Patricia Hodge - Again met through Lorna
Craig McLachlan - met through Lorna when they appeared in theatre together
Jon Voigt - Again met through Lorna
Stevie Nicks - lifelong fan. Went to see her show in Las Vegas and got to meet her afterwards
Sheryl Crow She was with Stevie when I met her
Lindsey Buckingham - met him when Fleetwood Mac toured over here in 2004
Mick Fleetwood - met him when Fleetwood Mac toured over here in 2004
Peter Green - met him backstage at a Fleetwood Mac show in 2004
Brian Wilson (not really on this planet!) - Again met through Lorna