Doof

A sound effect made by someone to emphasize when something is hit with high impact of any kind, be it a punch, a car slamming into a brick wall, a gunshot, or a high impact fart launching out of someones tight rectum with the force of ten typhoons.

You usually want to stretch out the "F" sound, as if it's a sniper rifle shot resonating through the air.

"Yo what's 'doof'? You keep saying that and it's confusing me."
"Oh! Allow me to demonstrate" *winds up punch and slams fist into their face* "DOOOOOOOOF"