I'm a huge underwear fan. I wouldn't call it a fetish - since it's not required for me to get off... but hot dudes in underwear - MAN!
I saw a dude the other day walking down the street shirtless. He was wearing a jock - and his shorts were sagged just enough to show a tiny bit of skin in the back, where his butt was exposed. Super hot!
I'll admit that I really really like sweaty underwear. I like to sniff it. I'm not after the the piss and crack smell... just the musky scent of a dude's sweaty nuts.