(The British and Canadian folk would understand this). When I was in college, I had a lady friend from the UK. One night we were both jokingly insulting each other and after she insulted me, I told her, “You better behave yourself or I will smack you on your fanny!”
Needless to say, “fanny” is not the slang word for a butt as it is for us rebellious American’s 🙂 But, after clearing things up she figured that was all what American boys can think of!