When one ejaculates onto the back of their own right hand, then procedes to backhand the partner on the face leaving what resembles a Riemann Sum graph.
Mason: My side hoe gave me blue balls so I came on my hand and gave that bitch a right-handed Riemann.
Connor: Damn, to be honest i'm more of a Left-Handed Riemann type of guy.
Get the right-handed riemann mug.