This is the term for when a girl hooks up with a guy, and then the guy becomes clingy and attached, forgetting that it was just "a good time." It is the combination of the words: Cock and Kukoo. It is used to describe when a man becomes clingy, similar to when a woman becomes clingy it is known as "dickmatized."
As soon as she slept with Ruben, she knew he was going to go cockoo on her. And she was right.