I guess it could be worse if the phrase were "taking a piss on my wife"... I once had a friend from England ask me very skeptically if you could really say someone was just "fucking with you" to mean someone was just joking around. So I guess it goes both ways.
I don't know why your friend didn't know that, but I would imagine most of us here in the UK would know what you meant by that. Not that I use it terribly often.