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4.
a guy who only thinks about his dick and goes from one girl to another.
john is such a cockbrain--he was just dating bridget but after he fucked her he dumped her for anne
by youngandinsane March 25, 2007
 
1.
when the male uses his cock as a secondary brain, often resulting in unfortunate choices and loss of girlfriend and or bodily harm caused by aforementioned girlfriend.
man i was so cockbrain last night, i had a great time but my girlfriend kicked me in the sack this morning
by IMMA MAN December 03, 2009
 
2.
When a guy hits a girl in the face with his penis. This often happens when a girl is giving a guy head. Usually an absurd gesture that a man will do to a promiscuous woman.
Guy: "So i was getting with Cheryl, and I totally cockbrained her!"

Guy 2: "Dude, she's got a shiner now!"
by Blob09 April 11, 2010
 
3.
A girl who is always talking about penises.

Kristen is being a huge cockbrain today.
by Johnny Hancock March 20, 2007
 
5.
someone who says something stupid cuz they been sucking to much.
person1: yo did u see the sky change orange?
person2: dog what is u talkin bout u gots that CockBrain!
by Matt "Big Dog" Dudley September 08, 2008