The measure of how intense your poop is after eating Mexican food. Based on the Fujita Scale (F-Scale) used to measure a tornado's intensity.
F0: Unaffected
F1: Little worse than usual
F2: Burns a little, not too bad
F3: Intense burning, but only one round
F4: Intense burning with multiple battles with the toilet
F5: Insane burning, seems like it will never end, nowhere near solid, soaks through the toilet paper, has you screaming and wishing the toilet had handlebars and cool air jets
I won't be able to make the party to tonight because we got Mexican food for lunch, I'm at an F5 on the fajita scale and won't be leaving home any time soon.