When a person has to poopreally bad and they can no longer buy time by farting
Jimmy let out a string of farts in an attempt to relieve the pressure of his impending poop. He carefully allowed one last fart to slip out. Jimmy then knew that the next thing to exit his ass would not be flatulence. He was out of gas.
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).