A less serious situation insult. Derived from the more common and overused "douchebag". Used to insult one of your closer peers, or perhaps your girlfriend, in a joking matter.
Kudos to mike for thinking of it.
Mike: "Hey, Anel, did you tell my mom she looks like Jabba the Hutt?
Anel: "Hah, yea. Even you said she does."
Mike: "Ahh, you douche mutant. Whatever."
The defintion of douche cookie is rather simple, it is basicly the same as calling someone a duche bag.
A duche cookie can also be used to describe the remnints of douching.
In this senario, Jack is a senior in high school that plays Uno and Magic at lunch in the cafiteria for fun. Sierra is a pretty popular girl who thinks Jack is pathetic.
Sierra: "God Jack, whats your problem, your such a little fucking douche cookie!"