Lock-Jamming Key

This key, when inserted into a standard household door knob, takes advantage of the design of tumblers to lock itself inside -- effectively making it impossible to pull out, and therefore, ruining the door knob.

WARNING: This is simply a proof of concept and should not actually be used to ruin someone's day. If you really want to destroy a lock, do it to your own door knob. Just don't complain when you lock yourself out of your house, because yes, it really will ruin your door knob, no, a lock smith will not be able to fix it, and yes, I will laugh.