During or after sexual intercourse, while your "partner" is in the cowgirl/reverse cowgirl position you unceremoniously back hand them to the bedroom floor or parking lot, depending on where the coitus is occuring.
Second definition:
While having sex in a plane or on top of a high cliff vigorous thrusting causes your partner to go ass over tea kettle.
Topended:
Becca was glad she had gone for the gold health plan at work. Getting "topended" into a moped will surely require stitches'.
Topending:
Marsha was only a flight attendant and wasn't suppose to jump with the other skydivers. However, "topending" is what she received from a randy instructor. Thankfully her fall to earth was short and filled with orgasms.
Topend:
Not being one to consider the needs of others, Bob would often "topend" his partner as soon as he busted a nut.
It is said of the situation where a person has the bad luck to make contact with his testicles against an undefined surface or object, intentioned or not.
Given the nature of the word, it is more appropriate to design cases where the interaction is made with a moving object, for example, a ball.
Although it is extremely painful for the victim, it tends to be considerably funny to people who witness it.
Today in the baseball game the pitcher took a nutshot; the baseball hit him in the nuts.
Man, I just watched the funniest nutshot video ever.