When a female provides a male sexual pleasure with her hand(s), using sunscreen as lube, until he has an ejaculatory orgasm. Using his semen, the male makes a mixture of semen and sunscreen, and rubs it on the desired area of his female partner. Then they go tan.

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