Also abbreviated to FRB, a fat rat bastard is an obese dirtbag who is the epitome of white trash. They sit on their asses the majority of the day and prefer budweiser as their beer of choice. Sweat accumulates in their belly buttons, groin, armpits, and the area between the man boobs and beer gut.
"Janet, get me a beer!"
"Oh Chuck, your'e such a fat rat bastard!"