when you put ur ass up to the jet on the side of a swimming pool and let the water shoot up ur ass then get outta the pool and shoot the water back out

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