Cross-cultural gaydar

This post is certainly somewhat not-PC, but I don't mean offense to anyone.  I was at the Paris Museum of Modern Art today (at a Keith Haring show, who was loudly and proudly gay), and saw a 30-ish guy wearing a small fedora, a scarf, and some canvas sneakers with a woven diamond pattern all over them.  I'm not really sure I would have thought he was gay in the US, but I would doubt whatever conclusion I came to much more than I would in the US.  I do think that it's much more difficult for an American in France to form an opinion about whether someone is gay.  There are certain cases that are pretty easy to deduce, such as the really skinny tall young guy that passed us on the street the other day wearing a plain white t-shirt three sizes too small and a pair of very light silk pants that were also three sizes too small, and had a flamboyant walk.