That reminds me...this is really bad....
Me and my roommate decided to play a joke on her mother for april fools.
We had it all worked out.
We wrote up a letter from the phone company saying that the phone lines were going to be cleaned out and that to please put a plastic bag on the receiver whenever she used the phone for the time specified as there will be dust blowing out through it from the phone lines.
She didnt exactly fall for it. But she thought it was the phone company who was playing the joke and called them and blasted them for the letter. It wasnt until later that evening, when she found a draft copy hidden under our schoolwork that she realised it was us.
Man, the look on her face was priceless!