Two men who have shared a particular sexual partner consecutively, although not necessarily in quick succession. The essence is, your Milk Brother was the last person to have slept with this particular partner before you did. (Like blood brothers have shared blood, milk brothers have shared milk, at least symbolically.)
Guy at Party: "Why does Javier's girlfriend get all tense, but also kinda flirty whenever Claude is around?"

Guy 2: "She used to bang Claude. In fact, Claude and Javier are Milk Brothers"
by Purveyor of fine expressions February 26, 2009
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Male friends who have shared sexual exploits (ie. having sexual intercourse with the same woman at the same time.)
Carlos & Diego are milk brothers; when they go out to hook up, they often bring back one chick and both do her.
by JohnnyKi July 15, 2005
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when two black men shoot their load into the same white women during the same instance of sexual intercourse.
We were only normal brothers until we bhad sex this girl at the same time and shot our load into the same pussy and then we became Milk Dud Brothers.
by 7878787878787878 December 21, 2006
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Also Known in some cicle's as Die Milch Brüder

AKA..The Hardest Techno band ever..Formed by an Auspicous meeting between a genuinely genius beat master and a impeccable Wordsmith in the DC area.

*There are many rumors about the origin of the name, but the group has kept the secret of its true meaning under lock and key.
The Milk Brothers are fantastic...they are harder than NeoPhyte of the Dutch club scene. The Milk brothers are great.
by Chrstoph Von Hund August 15, 2007
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