And as a gay man myself I've been groped by female colleagues before, had them come up and stand behind me and rub my shoulders/squeeze my back completely unwanted and I've done n o t h i n g about it, because nothing can be done about it.

That's the sad truth. Can't go to anyone and even if I did, they likely won't believe me, whereas she could retaliate and say I was the one that did the touching and she'd be believed with ludicrous immediacy. Life sucks, man.