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3.
A girl who is always talking about penises.

Kristen is being a huge cockbrain today.
by Johnny Hancock March 20, 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
 
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
 
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