One gorilla can be used interchangeably with on God.
Steve-"you promise you are going to come to my party tomorrow"
Fred-"I promise, one gorilla"
Used as a promise, and can be used instead of on God. It is a promise that isn't broken, guaranteeing something to someone.
Stan-"Do these shoes look alright on me, I wanna wear them to Stephens 80th birthday tomotomo"
Freddy-"yeah mate, they look great"
Stan-"promise?"
Freddy-"one gorilla"
Used as a promise, and can be used instead of on God. It is a promise that isn't broken, guaranteeing something to someone.
Stan-"Do these shoes look alright on me, I wanna wear them to Stephens 80th birthday tomotomo"
Freddy-"yeah mate, they look great"
Stan-"promise?"
Freddy-"one gorilla"