The latest Dork Tower unfortunately has as a ring of truth. Some gamers stink. Some gamers also have either emotional issues or stunted social skills. Not all, but some and they're common enough that some groups have had to take steps.
My brother is a member of the Philadelphia Area Gaming Enthusiasts or PAGE. PAGE has a rule, to attend one of their regular weekly gatherings you have to be invited in by a member. Requiring an invitation has the advantage of keeping both the Vampire roleplayers hissing on the doorstep and keeping out the people that aren't actually fun to play with.
You can just show up to a PAGE event of course. People do. I haven't of course but I have family in the group. If you are a "normal" gamer, then someone in the group will walk up and introduce themselves. They are of course sniffing you out. Often times quite literally. If you seem a good enough sort, they'll invite you in. But if you are dressing in floorlength black and smell of the grave, then don't expect an invitation.