when you and another woman begin to have anal sex in the middle of the night, you ride her around the room with your dick in her ass until you climax and then you yell "<your name> is cumming, <your name> is cumming!"

A jack off buddy (from 'cum' /'come', meaning 'semen', and 'companion'); a friend that you get together with for sessions of solo or mutual masturbation
Variant of: cumpanion (from 'companion' & 'cum'); jack off buddy & wank bud & JO buddy
Similar to: fuck buddy