It is used as a way to express extreme surprise at a fact. Derived from the word "fathom" which simply means "to understand". Fathometh is used to mean "You understand?" or "Riiiight?" but in old English (or King James English).
annoying, ugly, gets no girls/guys whatsoever, a nerd, weird
OR
talking about something u don’t like, something that someone does that pisses u off, anything annoying or irritating
Taken from the latin word 'meter' which means to measure, and the English word 'fat' meaning that jiggly cottage cheese bag around your gut and ass this word describes any kid of scale fat people use.
Alright chunky, get on the fatometer and make sure all of your sagging ankles make it on this time.