I heard that on a day when it has rained and a car is wet, if you put corn flakes on a car, when they dry they stick to it and ruin the paint. But that'* only something someone told me. It doesn't seem like it would work, but who knows.
http://www.prankplace.com/bumper.htm would be funny as long as he doesn't notice it when he drives away, its only magnetic. Some glue would work wonders on that though . Also if its warm enough out putting oreo halfs white side down on his hood will make fun little pin stripes that are a pain to remove.
Tie crab claw to fishing line and drop it down behind the lightswitch in the engineers office.
This will produce a particularly funky stank in just a few days.
Be sure to fasten it to the screw for later retrieval to remove the evidence.