A line used by sore losers who can't bear the thought of being left on their own in a party if their mates have tapped off - The fear of being without mates for a few hours and the thought of them not getting any action is too much to bear.
Phrase is used as a dirty underhand tactic as if to say "...dude, if you were my mate, you wouldn't go with her"
The rules of a flight squadron and wingmen dictate sometimes, one of you won't pull, and you accept that if the team feasts, you feast in their glory.
A true bro doesn't get jealous and fuck his mates' chances up cos he can't get some.
A true "bro" is happy for his mate when he gets tail and actually encourages it.
All for one and one for all, not NONE FOR ALL...
See also: Emotional Blackmail, Cock Block, Cock Blocking, Wingman
End of a houseparty, not many girls left. Nico doesn't really fancy said girl, he just wants to pull, but girl wants to pull dude and vice versa.
Nico: "I got dibs on that girl first, I saw her first"
Dude: "She's not into you dude, and we're kind of got a thing going on"
Nico: "Dude, don't get with her man, you're not a friend if you do... Bros before hoes..."
Dude "(What a tit)"
Dude: "Why are you following me and my lady home? Isn't your dad picking you up?"
Nico: "I fancy her man, she's Greek, and so am I"
Dude: "Well go fuck your sister then, this girl's been with me all night"
Nico "She liked me first. And I saw her first"
Dude: "...what the fuck...."
Nico: "Ok, lets share her then..."
Dude: "Lad, I wouldn't share a snickers or share my pint with you - what the fuck makes you think I wanna share a girl?"
Nico, pathetically: "Bros before hoes..."