When you see your brother jacking off and you join in

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

The art of rubbing only the finger tips all over the body to the point of climax

FInger tipping is the perfect excuse to not let someone win. If you just want to be first place just tell them that they were finger tipping