My first "hands on" experience with computers was at college. It was a DEC PDP-8, running FOCAL, and had the capacity of sharing <gasp!> FOUR teletypes! We only had three connected - budget restraints, even then! But we did have the optional 4K RAM expansion - a box the same size as the PDP-8 itself, full of ferrite cores!
FOCAL had a debug command. To run a program normally, you just entered GO at the "prompt", but if you entered "GO?", it would go into full debug mode, printing out everything it was doing, while it did it!
This not only resulted in reams of paper spewing out of the teletype (there goes the ole rain forest!), but also reduced the other teletypes to a 1-character per minute crawl!
Unfortunately, the reams of paper were something of a giveaway as to the identity of the culprit, so it wasn't really a very practical joke! But it did encourage you to write bug-free code - or at least, not use the debug option to, er, debug it, for fear of swift and violent retribution!