I have this fetish where I love licking a woman's underarms, to the point where she first feels ticklish and then becomes hot heavy and orgasmic...
You have a fetish which requires not the gal merely willing to go with it, but requiring her to have an odd nervous-system twitch that gets her orgasmic when tickled in the armpit (via tongue). I think that happened with a gal -- and you're thinking it's the norm with chicks. Hate to break it to ya, but it's not going to fly very often at all. :)
It's not really a fetish but a potential fetish that's a bit of a shot in the dark, because it requires more than someone willing.
A potential fetish: I love licking a woman's forehead IF it gets to the point where she gets hot & orgasmic. If it doesn't get her hot & orgasmic, me licking her forehead like Lassie, then it's not a fetish. Hence, I don't have a fetish merely licking a woman's forehead. It requires her to start flowing like a river if I do (not merely being OK with it; then just licking forehead would constitute being a fetish).
Where do you live?
I don't think he's into dudes' underarms, though! And he's gone... :)