When you laugh so hard you start to fart, which makes you laugh harder and lose control and you continue to toot along with your giggles.
Kwistin: (Laughing) Do you hear him out there muttering about Redneck Bingo? (Toot!)
Peaches: Whoa, what was that down there? Was that a butt chuckle?
Kwistin: Ya! I can't help it! (Increased giggling and tooting)
noun- a fart which produces noise from the butt cheeks slapping against each other
The awkward silence was made even more awkward when Bill released a smelly butt chuckle