Maximizing the size and shape of your gyatt, usually using exercise. You can do this activity by working out your glutes and pushing your gyatt back and your waist forward.
Bob: Yo what are you doing blud you look like your having a stroke Bill: Relax bro I'm just gyattmaxxing
The act of maximizing the size of ones posterior, or "gyatt", using exercise of the glutes and other methods, such as arching the back or artificial cosmetic surgery. Usually accidental, but can be done on purpose.
A word used when to decribe the absolute sheer size of someones ass. The word "gyatmaxxing" originates fron the word "lookmaxxing", which is when you do daily routines and exercies to make their appearance look better. So in other words gyatmaxxing is when you train and do exercises to make your ass huge.