Fun topic. I have a few stories.
I grew up in LA, so celebrities are not that exciting to me. However, when I was 8 or 9, my family was eating at an Italian restaurant in Studio City, my home town. William Shatner was a few tables over, and my folks INSISTED I go ask for his autograph. I lost the argument and approached him, which of course is invading his space, and not cool to pester anyone. Still...he was pretty cruel, and I was devistated. No autograph.
Years later, my high school band was doing this gig at the Universal Sheriton, some sort of LAPD community thanks luncheon thing. Shatner was the keynote speaker, and the band director was all excited, had us reherse the Star Trek theme, and when we started playing, he gave us a look that was pure evil. We stopped mid-piece. Probably the coolest thing about that day was when we were hanging out by the pool waiting around to go on, Telly Sevalise (sp?) walked by and kissed the hand of one of the girls, and he was incredibly creepy and slimy. All of us were amused, except the girl.
Shatner also blew off some event at my wife's university...he cancelled like 15 minutes before he was supposed to show up, so they dubbed him the Oversized Sausage.
The dude from Dukes of Hazard, the blonde one...can't recall his name, stole a menu from the Swensons I was working at, high school job, I actually ran outside shouting for him to bring it back, but he was gone by then.

And at the same place, I was running the store and in comes Scott Baoi (sp? again). The girl working with me was all excited, ran in the back and asked me if she should ask him for his autograph, and I said sure, celebs love fans, lol. A few mintues later, she comes back in tears. He clearly didn't give her an autograph.
Cool celebs I have known and met: Tom Poston used to come in every Sat. at the Swensons (seemed to be a TV star hang out of sort), and I used to talk to him as he ate the same sundae. Very, very cool guy. RIP.
Dick Wilson, probably known to most folks as Mr. Whipple had a son in the same Indian Guides group as me. Super great guy, I can recall making these fake bear claw necklaces in his back yard. He used to play a lot of drunks on TV, but was a lifelong non drinker.
I went to school with a number of kids who had celebrity parents, and one that I will never forget was Billy Bartey. Just a wonderful guy, loved kids, used to come to lots of school events, and he took a few of us out to see his modified car once, with the pedals raised so he could drive.
Last cool celeb story was Ray Bradbury, RIP. I went to this book signing at a SF bookstore in Pasadena, this was maybe 22 years ago now. He was really late, and the line was very long, but I was 4th in line. He comes around the corner drinking a Corona beer and smiling happily (at something like 10:30 AM). The first person pulled a manuscript out of her bag and asked him to read it. He politely said he couldnt do that, liability and all that, and then the second person pulls out a manuscript. Less polite no. The person right in front of me...yes...pulled out a manuscript, and he just blew up. So i walk up, he glares at me and askes me if I want him to read a manuscript, and I said naw, I just wanted to meet you, love your work, etc. All smiles, we talked for at least 20 minutes about his latest projects, had a great time, and when I finally left, the other people in line gave me really dirty looks.