Complement people on their shoes.

Ask the person in the next stall if there's anything swimming
in THEIR bowl.....

Scream " Oh my GOD! What the hell is THAT?"

Kick in stall doors, camera in hand.

Run around naked yelling "Where's the fish?"

Replace rolls of toilet paper with rolls of sand paper.

Remove stall doors.

Glue seat and cover down to bowl.

Place signs warning of 24 hour video surveillance.

Put itching powder on the toilet seats.