I dunno, leave some child porn out on the photocopier maybe

( glued eel /questions/questionsyoudliketoask/post1648081, Wed 20 May 2009, 9:18, archived)

make 200 copies,
then put them back into the copier. So the next person who makes a copy gets porn on the back.
(PsychoChomp, Wed 20 May 2009, 9:22, archived)