It always feels a little odd stopping someone in the middle of a crowd and asking if you can take a photo of them. At least at PAX, they know why you're asking and you know why you're asking, so that makes it slightly less strange. And I think I'd feel worse if I didn't capture some of the excellent cosplay wandering the expo.
My favourites are the Pyro in the lead image here, and the gun-metal Iron Man suit in the photos below. The latter was particularly impressive with its glowing eyes and chest-mounted power source.
Despite taking photos of every costume I've spotted so far, I know there are great ones out there I missed. If you've been doing the rounds at PAX yourself and snapped a few shots, please share!