Dirty Surfboard

When you are at a party/large gathering, and you have to drop a poopie, so you proceed to turn on the bathtub/shower at said party, and proceed to take large poopie/poopies in the tub. Wait a few hours for the bathroom to flood, and vuala! A dirty surfboard!

"Yo bro I just rode the waves on that dirty surfboard you made in the bathroom. You pooed a fat one out."