Oh, *that* look. Alas.
I don't get it half as regularly as I used to. I started my convention explanation including the "We've got to be sure to keep the partying down to a dull roar, because we're sort of going to entirely take over the hotel, and we don't want to accidentally get kicked out." It's sad that something like that gets more respect than "Yeah, I'm going to hang out with a whole bunch of people who like the same books and movies I do -- why yes, science fiction and fantasy..." but evidently there's this misconception that there's a whole lot of dry dull people mixed in with completely socially incompetent people*, all sitting around droning on about books in the monotone of the guy everyone wants to tell to STFU, but it wouldn't be polite to.
So I mention the partying first, and *then* mention the common interest that's bringing the partiers together.
And thank goodness for Weird Al for making at least a taste of filk mainstream.
* There are a quite a few people in fandom whose social skills are, admittedly, not up to the mainstream society social standards. But that's not necessarily a complete barrier from normal social interaction in fandom. Granted, a lot of social interaction with them then becomes tip-toe-ing around their Issues, but the things they have to contribute (they may write, filk, draw, or game absolutely wonderfully) are not completely ignored because of their social ineptitude.