My father stole his father's silly-threat line:

Call: "I'm going to take off my belt and the you know what'll happen!"
Response: "Your pants will fall down!"

It's an interesting cultural shift in the years between those generations--my father understood the corollary growing up ("when other fathers say this it means X, but when I say it, I will only ever mean Y"). But to my sisters and I, we were merely being threatened with a mooning, and we literally didn't understand that there was a violent meaning behind "taking off one's belt" until we were nearly in high school.