Word used to describe someone who so utterly annoying, and queer. Instead of cock, cocko is used to emphasise their 'gayness'
Isaac: Man I am so cool, you WISH you could be like me
Sal: PFFFT whatever, why would I? Your such a loser.. look at your hair you queer!
Isaac: your just jealous man, everyone is
Sal: okay, then your a cocko