A beautiful term for an extremely Foul smelling fart. The term is made funnier if the fart sounds like quacking duck when expelled from the rectum. Though an SBD can still qualify as a Butt Duck if it is especially foul (emphasis on the word foul/fowl for comic effect). See frequently activated rectal tremble and shit flavored air.

Got the covid-19 vaccine

the sound produced by air rushing past an anus resembling the sound of a duck.

A baby duckling that is lodged up the anus after sitting on it at a very young age.

stinky farts that sound like ducks coming out your ass

when there's a very large crack head duck stuck up your ass.