The act of one person taking a dump normally on a toilet while another person sits on their lap facing them and takes a dump through the space between the first persons legs.

A tandump can be performed either consensually or by ambush. In an ambush tandump, the assailant initiates a tandump by climbing over a stall wall and dropping down onto the unsuspecting pooper.

When you eat dirt for the first time and leave your family to build a shack in the woods