norm. If I see a guy in a speedo yeah I'm gonna look but I'm not gonna stare at him or take a pic without asking. Heck, I saw three guys at Fantasy Con dressed in full Gandalf, and two hobbit outfits. Not immodest in any way, but I still asked them if I could take a pic.
I'd say if the people are publicly performing or putting themselves on display it's okay, but if I don't know the person I'll ask to take a pic no matter what they are wearing. It's just polite, I think.