When you fuck a girl in the butt, and she puts diarrhea on your dick, and then you take it out and put it in her pussy, and the wetness causes a queef. That's a zizzle fart.
Caitlin:"Okay, so last night night, I did the worst thing ever to my man..."
Jennie:"What'd you do to him?"
Caitlin:"Well, he was fuckin me in the butt, and I just laid a zizzle fart all over his cock..."
Jennie:"Oh, that's siiiick..."
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).