I never seem to be able to come up with much, but:
Last year my best friend still lived with us and at like 12am he went to take his girlfriend home so I rushed and changed the door knob. He came home a little later than expected and he had just happened to call me as he was coming home to tell me something so I was on the phone with him as he tried to unlock the door. I found it hilairious! It still makes me laugh the way he reacted!
This year I kind of did the same thing to him. We were hanging out at his house so I took his house key off his chain and I hid it in his car. When he comes home from work tomorrow he will be lost

I know he will know I did it so when he calls I can just tell him where I put it.
Now if I could just get DH....