The act of defecating inside the
water tank of a toilet.
Step 1: Go to the home of your mortal enemy. Ask to use the bathroom.
Step 2: Approach toilet and remove the water
tank lid.
Step 3: Step on the sides of the toilet and squat over the water. Carefully take a massive dump. Wipe your ass and dispose of toilet paper in the trash bin.
Step 4: Place water
tank lid back on the toilet.
Step 5: Escape.
What happens? With each resulting flush, it will fill the bowl with a chunky brown water. Its the gift that keeps on giving :)