Too bad the translation’s not really accurate here. It should say “god damn!” GYATT DAYYUM

tl;dr: gyatt is almost exclusively used to mean, “god damn, phat ass.”

Except it is accurate, in shorthand and meaning. Gyatt started off to mean “god” and people would even say “gyatt damn.” Then it moved to be fully “gyatt dayyum” to mean “god damn” as you noted…and then abbreviated to just “gyatt.”

Then it evolved to the present day where gyatt is mostly used to say, “god damn, that’s a phat ass” or some variation. When something is terrible or your disappointed, you don’t really say “gyatt it” or even “gyatt dayyum it” to mean “god damn it” or if you’re pissed off at someone, you don’t say “gyat you / gyatt dayyum you” to mean “god damn you.” But if someone with a phat ass walks by, you’ll say “GYATT,” to mean "god damn, that’s phat ass.