alright the one that i was gonna post is a bit complicated so here goes..
find a teachers car and get into it somewhow or pop the hood. cut the wire that runs from the battery to teh ignitition to the starter motor. u need to have some of the wire they use in icemakes for this (it heats up when current goes through it to make the icecubes square) you put that in where u cut the wire and complete the circuit. take teh wire you just ut in and wrap it around the fuse and body of an M-80 or similarly powered fireworl. when the car is started....current goes through wire....makes wire hot....lights fuse...BOOM, then circuit is broken = no car start
lots of smoke and a scary bang
freaks ppl out like nothing else