Stands for one of the following forms of motherfucker: motherfucker, motherfucking, motherfuck. The form that is used depends on the context of the situation.

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

mf has 2 meanings, often used as:

(i) Mother Fucker
(ii) My Friend

definition (i) is more commonly seen in chatrooms; whereas definition (ii) seen in multiplayer games.

if someone uses mf towards you, it's best to pretend you dont understand, so they will explain - either (i) or (ii). Since you dont want to just start insulting them.

this word is used when youre tryna describe someone who hurted you so bad you can't even say his name. You call him "mf" short for mother fucker because he is the worst fucking person, he fucking played your feelings, he led you on, he made you fall for him, then he'll leave you with the "let's just be friends" so yeah fuck him.

This is a term for Mother F*cker or Mother F*ckin that can be slipped into any abreviated or slang phrase without offending the majority of the public.