gorilla math
Bad math. Very crude, bad math, often performed by someone who thinks they know what they're doing.
(From Rounders)
Mike: "So, what do you owe him?"
Worm: "I don't know, by his crazy fuckin' gorilla math... like fifteen."
Mike: "So, what do you owe him?"
Worm: "I don't know, by his crazy fuckin' gorilla math... like fifteen."