A small explosion between the legs, composed of vapourized poop particles.
person 1: ewww dude did you fart?
person 2: yes indeed i did, you heard the explosion didnt you?
person 3: yes, eww it smells disgusting
person 1: omg bro dont breathe it in, you realize you are inhaling particles of his poop when you smell it!?
person 3: kill me now.
person 2: MWAHAHAHAHAHAHA!!!!! smell my wrath! :D