Another favorite of mine which I find much more destructive (read
effective) is to mix a quart of gasoline with a tube of valve
grinding compound and then pour it into the offender's gas tank.

A less destructive revenge tool is Anti Seize Compound. Liberally
apply to the inside of the outside door handle of a car. When 
your "victim" opens the door...ASC all over the hand. As those
of you with experience know...when you try to rub ASC away...it
just spreads and spreads   ;-)

Of course these are somewhat "harsh" means....but sometimes
ya gotta do whatcha gotta do!!

Ric