Unintentionally farting while walking. A short, but loud fart comes out with each step. So it sounds like a motor boat engine grumbling as you walk.
My buddy was so embarrassed cause he was motor boating in the cafeteria.
In Europe, its a marlboro cigarette dipped in opium and then sprinkled with pot. If its done right, it looks like a green-hairy cigarette.
On his first trip to Amsterdam, John smoked a jumpoff cigarette called an OJ