Nice:
-All the BSG cast and crew are amazing. Michael Hogan took the time after a bsgo concert to take photos with me, and was making sure the picture came out good, and asked if I wanted another, etc. Nicest guy! Was hugging me and so happy to be there. Seriously, that cast and crew are what made that show so amazing.
-Star Wars cast. They go through a lot. Very few celebs get that much put on them. Mark is hilarious, and loving, and warm with fans. I've seen him for star wars stuff, batman, etc, and he's always so much fun.
Peter Mayhew has a lot of health problems, which a lot of people take as him being mean, or rude. he's simply in pain. If you get him earlier in the day sometimes, he's got more energy. I've talked to him for a good ten minutes before, and he was very friendly.
Kenny Baker and his wife/family are great too. Helped them move his signing table when I got into comic-con early one day. Obviously, it was a harder thing for someone his size to do, and my bro and cousin were stoked to help him move it! He's also very chatty when you get an autograph.
David Prowse - I met him before episode III. He was all alone. Darth Vader was all alone on the autograph pavillion of comic-con. Not enough people even knew who he was. So I took like 30 minutes and just gushed to him, and sat with him, and chatted. He told me all about how he was trying to get hip surgery, and had a lot of hope he was going to get to play vader one last time for III, as soon as he was all healed from the operations. He seemed so depressed when I first saw him, but by the time I left, he had shook my hand several times, and signed for me, and actually had a bit of fire back in his face. Clearly, it pained me to hear later about how George treated him with episode III, realistic or not, and how hurt he was by it. Rough position to be in! But regardless, i'll always have that great memory of talking to darth vader, all to myself, in the middle of comic-con as nobody else knew who the hell he was. Crazy!
Bulloch - amazing, again.
Warwick Davis - One of the nicest guys ever. Joked around, and as many have said, he cracks jokes with you to let you know you don't have to feel odd about his height. he makes fun of it so that you will relax, and realize he's just a guy. Still, I was totally star struck by him. Willow, Wicket, Lep., etc. So fun! Such a wonderful man.
Uncle Owen.. i forget his name.. Phil something. He was very very old and ill when I met him, but I'd always go say hi at the con, and the first time I did, he signed for me. Very nice man. Few years later, my little bro went to get an autograph as they were packing up, and his wife told my brother that he couldn't sign.. and wanted to know if she could sign for him since he was so sick. My bro said no, and just said "just let him make his mark. I'm not gonna sell this. I just would like to have something from him!" And Phil smiled and tried to scribble out a sig. I think he died a few months later at the age of 89. Wonderful man. So glad I got to meet him.
Elijah Wood - Bumped into him and some guys who were crowded around him right before fellowship came out. Didn't even know he was playing frodo! Had loved him in some other movies, and said so, and he was like.. "thanks man! means a lot! just try to keep it down, or other people will swarm me!"

Sure enough, even at that point, it was nearly impossible for him to walk the con floors!
Sean Astin is amazing too. Very friendly man. All of the hobbits were, from what I could tell, even though I just stood back and listened to Dom and Billy.
Star Trek. Walter was very nice when I got his autograph! I have a picture of Majel from when i was a little tyke. She personalized it for me, (thanks to my bro i think) and it is one of my favorite autographs! Brent Spiner is really funny too.
I've met tons of celebs at the con, or other places. Most of them were always good.
The bad?
Eli Roth - came across as a total ******. Wont say how. All I'll say is I wouldn't trust him with a 12 year old girl in a million years. I saw a side of him before he got super popular that just totally turned me off from ever wanting to meet him again. Total dick, and slimy/creepy as hell.
Lou - as everyone has said. Some days he's better than others. And some days, him being deaf has more of an impact on his mood than anything. But nothing excuses the amount of money someone like him charges for being a complete tool.
Jake Lloyd. Can't stand him. One year, our venom for him was so bad a friend of mine saw him get out of a car at comic-con, and he said "Hey! It's Jake Lloyd!" and jake turned and smiled. My friend promptly gave him the finger, and did his best "che chabba chawa!" before screaming "Hey! It's the kid who ruined star wars!"
Honestly, I don't recall that many BAD celeb meetings.
The good ones are so wonderful they usually overpower any bad ones.