For me it's the stuff from OotP. He watches Sirius for a fair while in that big kitchen scene, and their interaction mirrors the Molly/Arthur interaction quite a bit. Plus Remus is alone, and seems to have only ever had his schoolfriends in his life... okay we could be missing a lot of his inbetween story, but there is the impression that they (or one in particular, who knows) meant a hell of a lot more to him than we would expect. Maybe it's just too sad to think that he never got any shagging in at all :(

But the polite and understanding gay man thing? Hahahaha. My best gay male friend is a Geordie with a foul temper who swears incomprehensibly and gets into fights when he has too many beers.