The guillotine

A 'practical joke' that involves lifting the seat of a toilet, and intricately defecating on the front lip of the bowl. You then delicately place the toilet seat on top on the freshly laid nugget, and evacuate the stall. Ideally, your intended victim will come along to enjoy their peaceful abulution, drop their pants and proceed to sit down. The result of their bodyweight on the toilet seat will sever a section of turd and eject it like Mary Antoinette's head into the victims awaiting pants. Everything going to plan, you will have successfully shat in someone's pantaloons while they are wearing them. And probably irrevocably burned any bridges of friendship in the process.