You're back? Cool. Okay, so...
The San Diego International Comic Convention (and really, any of the large media conventions, but SDCC more than most) is simply crawling with famous people, ranging from your stealth famous (most directors, producers, and writers) and formerly famous (the obscure character actors and aging child stars selling autographs near the rear of the dealer's hall) to your currently huge famous (the cast of True Blood) and your geek darlings (the cast of Eureka). Where someone falls on this scale during the convention may have absolutely no relation to where they'd be on the scale out in the non-convention world, although it mostly works as an enhancement of fame, not a reduction. Britney Spears would be mobbed at SDCC, no matter how few fans admit to liking her music, but I doubt Felicia Day is going to get stalked by paparazzi if she tries to go out for a burger.
If you attend SDCC, the odds are good that you will see famous people. Buying breakfast at the deli! Crossing the street! Trying in vain to get some shopping done in the exhibitor's hall! Walking really, really fast toward the nearest bathroom! Standing on the sidewalk with a stranger's arm around their shoulders, smiling graciously for a camera! This is going to happen. It is unavoidable. And I, from the bottom of my heart, make this request of you:
Don't go batshit because you're breathing the same air as a famous person.
Nathan Fillion is awesome. He's a funny guy, he's nice, he's considerate, and he worked on one of my favorite horror movies. He does not, however, give off a chemical signal in his sweat that causes my ladyparts to explode and my brain to stop functioning above a third-grade level. Stephen King is one of my personal heroes, and wrote three of my five favorite books. That does not mean that he intended Annie Wilkes from Misery to be taken as an ideal of fan behavior.
I am, by the standards of any media convention, a fourth-string celebrity at best. I'm a writer, which makes me invisible; I don't wear miniskirts or preach controversial opinions or have a TV show based off my work; I'm relatively new on the scene. I'm a very small fish, and I appreciate that, because even at my current, erm, fish size index, I've been stopped while walking someone, interrupted while very clearly doing something, and, my personal favorite, grabbed—physically grabbed, by people I do not know, and did not consent to being grabbed by—on my way into the bathroom.
Now, I don't know about you and your strange Earth ways, but on my planet, when someone is walking briskly toward a bathroom, they probably intend to do something involving bodily wastes and a toilet. Consider that I drink roughly four liters of Diet Dr Pepper a day during the average con. Now consider the danger of grabbing me while I'm on my way to make some room for more soda.
And there are people who say "well, you signed up for this" when a famous person, regardless of fish size index, has issues with being grabbed or interrupted or otherwise poked at in public. But at the end of the day, no one, no matter how famous, no matter how big of a fish, signed a contract saying "anyone who wants to can now grab you at any time, have a nice day."
These are the circumstances under which it is acceptable to touch a stranger:
1. If they have a hornet or something on their shoulder and you're brushing it off.
2. If you're shoving them out of the way of a Martian ray gun blast.
3. If they're standing on your foot and you need to tap them in the shoulder to get them off you.
4. If they just dropped, like, their wallet or something, and shouts of "Sir? Sir!" or "Ma'am? Ma'am!" aren't getting their attention.
There may be others for this list, but you get the idea. These are the circumstances under which it is NOT acceptable to touch a stranger, regardless of whether they're famous:
1. Because you want to.
2. Because they're there.
3. Because you feel like you have a personal connection to them, even though you've never met.
4. Because then you can tell your friends about that person you touched.
...again, there may (will) be others on this list, but you get the idea. Saying "Excuse me? Mr. Whedon? I love your work, could I get your autograph?" when you see him in the hall is cool. Following him into the men's room is not. Camping out in front of his hotel, also not. And the coolest thing of all is taking "no" as a legitimate, and understandable, answer.
Please, treat everyone with the same respect you want applied to you, whether they're famous or not. Do not separate people from their friends and family, or grab them, or stop them from getting to the bathroom. If you wouldn't let someone do it to you/your significant other/your kids, don't do it to someone else.
Don't let proximity to fame make you batshit, and these conventions will be a lot more fun, for everyone.