I've seen that guy so many times it's sickening.  The last time was at a burger joint.  Barry Corbin and his family came in (they live in the area).  I was tempted to just stop by the table and say a brief, "Hello Mr. Corbin, I love your work." but I thought better of it and decided to leave the guy in peace.  Then that guy and his buddy came in.  Barry is impossible to miss.  He's a very loud speaker, and his voice is so distinct that nobody can help but notice him.  The murmurs of, "It's that Northern Exposure dude" and such began to waft over to my table, and I knew a painful scene was about to be witnessed.  Sure enough, they both approach his table and call him "Maurice" because they don't know his real name.  He was nice enough, despite their idiocy.  I felt like I had to do something to make up for what they'd done, so as I was leaving, I gave him a nod and called him, "Mr. Corbin." so he could at least have someone who knew his real name.

That must be a major annoyance for celebrities who are known for a particular role and little else, despite their vast portfolio of work.  How many times has Mark Hamill been called Luke to his face?  Too many too count I suspect.  If you can't be bothered to learn their name, keep your mouth shut!

 I like celebrity watching at Comic Con. One year I was in line to pick up my four day pass, and outside by one of the doors was this familiar looking guy that was puffing away on his cigarette like crazy. He was puffing, puffing, puffing, and I was racking my brain trying to remember where I'd seen this guy. Finally he takes one last puff, stubs out the butt and runs back inside just as I realize it was Bruce Timm. 

Or the time I saw Paul Bettany with kids in tow (Jennifer Conolly (his wife) was doing a panel for The Day The Earth Stood Still) walking through the aisles in the old comics section while talking on his cell, Or having a thoroughly stoned Seth Green stop by the booth I was working at to check out the Clockwork Orange Alex figure we had for sale (only to have my friend (who's booth it was) chase him off when he was fumbling for his camera). Or having Peter David swing by the booth after the floor closed so he could take a few pictures with the Ultimate Thor hammer we had on display. Literally bumping into Ron Perlman out in front as he was trying to find his ride. Being hit on by one of the Marvel female writers line up, when really all I wanted was to get an autograph for my sister who was a big fan and couldn't be there. Running past Joshua Gomez (from tv's Chuck) and his girlfriend in the parking garage as they stopped to pose for pics for a few fans. Being shoved up against Olivia Munn (yeah, I know, horrible, huh?) by the crowd as they surrounded her in front of the con while she was trying to tape something for G4. At the time, I didn't know who she was, and I was really just trying to get to my car after a very long day. Winding up in a hotel room suite during Wondercon talking to the head of Boom Studios and a few comic book writers and artists about anything and everything during a private party. 

BUT...my absolute favorite, and most random, had to be when my buddy (who lives down in SD) came by the hotel and took me and another friend to this little dive bar nearby. We were there for about an hour when the DJ said something that sounded like a major DJ group was going to be stopping by for a visit. We thought we were hearing things..but we stayed. We were rewarded with a small (about 200 people) concert put on by Daft Punk who had played Petco Park just the previous night and were in town for the Tron Legacy panel. Turns out they knew the local DJ, and it was his birthday, so they decided to play for about two hours! No cover to get into the place. No prior annoucement or ticket sales. It was a totally last minute thing they decided to do..in full costume. I have about an hour's worth of video of the show still on my computer. 

Honestly, I've seen so many celebrities in my travels and different working environs (don't get me started about The Bob Hope Desert Classic), that I just don't bother asking for autographs or photos or anything anymore. Why? Because they're just people like you and me. If you're a fan, you can mention it politely without having to go overboard about it, AND if and when it's appropriate to do so. The same as any other social situation. They'll appreciate that more than having a paper and pen shoved at them. 

I've seen a few celebs too. I'll be honest usually I just keep walking, even in NYC sometimes folk'll just ogle. If they're at an event promoting something or signing stuff yeah I guess it's ok to approach them but that doesn't interest me personally. A long while back  I actually walked by Arnold and he was/is one of my childhood movie idols but I still couldn't bring myself to chase him down and ask for a picture (which is what I'd want not an autograph) or something. Seems so intrusive

 I got over the "autograph scene" after I put on my own fest aboard the Queen Mary.  I met many James Bond and other related celebrities.  We even had the entire cast of Kill Bill (the movie was being released.)  After talking to so many actors, writers, etc. I just lost the thrill.  Some are generous with their time, others area pain in the arse and, really, it is a bit silly to want an autograph from a guy who makes his living play acting.  Like Robert said, a good story is just having a simple conversation that is not forced with someone who admire.  

I was working at a locksmith shop in Texas when Barry Corbin came in.
He was buying padlocks for his ranch in Ft. Worth (this is when Northern Exposure was still on.)
I waited until after the transaction was complete, and then let him know I really liked his work, especially in War Games.
He kind of stared me down, grunted in what I can only expect was disapproval, and left.
Not sure if I was being "that guy", but he made me feel like I was.

About a year ago I was in a local restaurant and saw Adam West.
Now, I love this guy, and was tempted to go up to him.
However, he was at a table with his wife (I assume) and another couple.
Had he been alone, I might have chanced it, but I felt that he should have his peace.
So I was able to avoid being "that guy".
Next time, Batman, next time!

And lastly I was in LAX a few months ago and saw Thomas Hayden Church.
Thought it was cool seeing Lyle in an airport, plus I think he is genuinely funny.
He was standing alone, and back by a wall just kind of hanging out.
As I debated whether or not I would be "that guy" if I went and just said how much I enjoyed his work, I watched as "that guy" appeared out of nowhere.
"You're that dude! Y'know, that, that dude from that movie and that show!"
Needless to say, he was less than impressed.
In fact, I think it is safe to say he looked kindof pissed off.
Decided that after he had been subjected to "that guy", I would just leave him be.

BTW - If any celebrities are reading this, just know that for every "that guy" you have to deal with, there are at least a half dozen of us who did recognize you, but choice to let you have your space.
You're welcome.

I was at Scapercon 2002 and Virginia Hey (Zahn) was attending.  It was a small con and by the third day everybody but my roommate Sidhesong had stopped by her table for a chat and an autograph.  Sid was too shy to meet her so I got an autograph for her.  Ms Hey told me that my roommate was being silly and she should stop by and say hi.  I bodily dragged Sid to Ms Hey's table and at first she was shy but soon the two women were talking like old friends.

The next day the con ended and Sid and I saw Ms Hey checking out at the front desk.  Sid went over to say goodbye and unfortunately mentioned another Scaper who had been rude to Ms Hey at a prior convention.  Ms Hey frowned and exclaimed at how angry she was about that.  Sid was so embarassed she started to cry and turned and ran down the hall.  I will always remember Virginia Hey chasing Sid down the hall yelling "Come back, I'm not mad at YOU!"