Hm, I think that the fandoms depend on the area/con you're going to. At Anime Detour, the biggest anime con in MN, I went to multiple Homestuck photoshoots- and everyone was so sweet! I wasn't even cosplaying Homestuck(I was doing fem!prussia), I was even by myself because my friends weren't interested, and just everyone was really nice, and mellow- there were no buckets and screaming of profanities.
That versus Anime Fusion, a brand new con this year, I think about half it's attendants were Homestuck, and while a lot were nice, there were a few younger ones that needed to take a chill pill, I'm guessing it was their first con and they weren't with their parents, so its easy to get carried away.
So I think it all depends on the con. Bigger, more established cons tend to have older attendants, while newer, smaller cons tend to draw in younger con-goers who are away from their parents for the first time.
Next Convention: Anime Detour
Scarlet Witch- Avengers: Age of Ultron
Laurel Lance (Black Canary)- Arrow