If you work in construction there's lots of practical jokes you can do,,,,, like send some new young guy to get a long stand from your friend!! your friend say ok ill get it now for you and let the guy standing there. your friend comes back and asks the young guy was that stand long enough??
also the cement back or plaster bag trick!! i love this one!!
http://www.youtube.com/watch?v=GDRwTcfRE-g