I had a former buddy who would have his face planted in mine most of the time we were having sex. He turned me onto it a bit and now it's one of my hot buttons. Some guys like the natural/musk smell as an aphrodisiac of sorts. But I'm much more likely to get my face in there if they're clean. I like a man with plenty of chest hair anyway, so a guy that shaved his armpits would be hard for me to be attracted to.