Since the conversation has already sunk this low, a couple of comments.
A few days ago I received a jokey quiz for men on matters sexual. Answer A was the romantic, Answer C the real man's answer. For example:
Spending the whole night cuddling a woman you've just had sex with is:
A: The best part of the experience
B: The second best part of the experience
C: 100 bucks extra.
Anyway the last question is apropos the specific subject
Onanism(Don't look Jackie):
A woman who is uncomfortable watching you masturbate:
A. Probably needs a little more time before she can cope with that sort of intimacy.
B. Is uptight and a waste of time.
C. Shouldn't have sat next to you on the bus in the first place.
Moving swiftly on, many years ago when the word "wank" was unknown in the US, a colleague of mine moved to the States and formed a soccer team known as the Westchester Wankers. And no, apparently the team didn't know what it meant either. I think he told them it was some technical soccer term (like dribbling?

).
But I also agree that it is a very flexible term and is used quite frequently in UK.
Rod