How do you avoid fat ass from sitting sooo long?

Large buttocks. The large buttocks are not due to sitting in a chair per sé. Your buttocks has not magically molded to the shape of the chair. The problem is that you are sitting too long and not exercising and burning up enough calories so that there is a fat excess in your system. Get out of your chair and start moving! walk during breaks and lunch.
Physical Activity. I agree with dr. Bolhack. A large derriere isn't from too much sitting, it 's from too little activity. Go shake that booty with aerobic exercise.