Depends on who you're with.
That depends, asking on the way to McDonald's for a first date is unacceptable. Asking in the middle of a passionate fuck might be ok.
certainly not too far, i'd gladly oblige. but maybe it's something that requires some mutual trust, not to be asked first time in the bed
I'm basically straight, but I have done it to a few guys and have had it done to me in return. Never had the pleasure of doing it with a woman, though.