This is an interesting point. Cons make this complicated in some ways, because we're there to connect with fellow fans. And if you spot someone who's obviously part of your somewhat-obscure fandom (due to a costume, or a t-shirt, or because you were in a large-group conversation and they laughed at your totally obscure nerdy joke...) that can create a false sense of intimacy.

Sometimes, you can connect with that person and it's AWESOME and you make a new friend. But when you approach that other person you need to take it slow and absolutely accept no for an answer. Having that connection sometimes lets you move very quickly from "stranger" to "friend," though, and that's part of what I go to cons for.

(None of which even remotely excuses Randall Garret, mind you.)