Person who has an abnormally large phallus, knows they have an abnormally large phallus, and acts like they have an abnormally large phallus.

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

Delow is a UK term for down low or given as a name for sum-one to keep stuff on the down low.