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2.
When someone is crazy, or insane. Off the deep end. Berserk. A nutter.
"Watch out for Ethan, he's totally berko!"
by Colin Kelly March 25, 2006
 
1.
To lose the plot - usually with a lot of cursing, swearing and wild gesticulating.
"Bob is going completely berko over that mistake!"
"His team lost the match and he just went berko!"
"If I don't get served next I'm going to go berko!"
by Schlub September 30, 2007
 
3.
Too 'lose the plot' as to say. Yell abuse etc...

Mentally or emotionally upset; deranged: berko with grief.
One that is violent, upset, or unrestrained.
A situation has not worked out as you hoped (you go 'berko')
by Neri August 07, 2006
 
4.
1. An affectionate abbreviation of the name of the hertfordshire town Berkhamsted, used by the working class and middle class residents alike (see berkhamsted).

2. A word used to describe someone as racist, xenophobic, and totally anaware of any world outside of Berkhamsted. Specifically coined at the University of Sussex, in the mid-2000's. Particularly used by drama students.
1. "Come on Berko! Come on Berko! COME ON BERKO!" - Commonly heard on saturday afternoons at the Lilywhite 'stadium'.
"Uh, yah! I, like, go to Berko girls' school"

2. -"Are there gunna be any darkies there?"
-"God, you're so berko"
by Kyle Ross Richardson May 18, 2007