Pretty easy really. Although its a bit harder to do these days with caller ID and such but what is the best crank call or phoney question you ever asked some one?
My friend and I used to call up random people out of the phone book during the holidays and say that our mothers didnt know how to cook a turkey and asked if they would explain it to us.
It was amazing how many " Oh you poor thing, sure I'll tell you" we would get.
Pretty messed up, I know.