I leave my underarms natural. Downstairs, I just trim what would stick out beyond a bathing suit. I do shave my legs though.
I don't know if it rises to the level of a fetish, but I do
like it. My skin in both places is a little on the sensitive side and it feels really nice to have fingers caress and run through it during foreplay (including when it's just me).
I would say it's not something preferred by most guys. If I were to start a thread about who likes to be tied up and whipped, 10 guys would chime in and say that's hot. If I were to start a thread asking who doesn't shave their underarms, 10 guys would chime in and tell me how disgusting that is and how they're on the verge of vomiting.
But... I don't have to worry about pleasing the whole world. Just my boyfriend, and he's into it, so all is well
I've never been hassled about it (even at the pool you wouldn't notice my underarms unless my arms were up over my head. It's natural, but not super long or anythign), but I have had a few people ask (usually girls) out of curiosity why I don't. It's a bit of a lie, but I just say that my skin there is really sensitive and even if I use an electric they poke me and I get a little rashy.