Someone who gives unsolicited correction to others social media posts, ruining any humor the post otherwise might have had. Also see: nit-picker, know-it-all, pedant or

foreign (UK): clever clogs.

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