Boxers, which I always associate with my ex-husband (but it seems 96% of men wear boxers).
When the time is right, I'm getting him boxer-briefs. I've always liked the look of them. Besides, his calorie-burn yoga gives him an amazing definition that needs something with more cling.
Gay Unicorn: I don't prance, I mince!
(Sorry, couldn't resist. Heh-heh.)