-Change their login name and forget what they changed it to.
-Bake their powerbook at 450 for 10 minutes
To perform an applestamp, close said notebook, raise it to a proper angle, and strike the offending user on the side of the face or about the head in any manner you deem appropriate.
The result, if done properly, will be the apple logo on the dolt's cheek. There for always, to remind them that yes, they are one of the .04% of people that are too stupid to use a mac.