I'm not going to try to come up with a good idea for the webcam... but I do have an interesting idea to get back at them.
A friend of mine attends college up in Northern Florida and one of the people on his floor always had people bugging him with things, and he pretty much wired up a 12volt (I think) battery to the metal knocker on the door... so when people would knock on the door, they received a very unexpected "shock" hehe... they quickly stopped knocking on his door.