A person so overweight they stay inside all day long. Usually due to crippling depression brought on by morbid obesity and/or ugliness.
Person 1: Some chick bought my movie collection but she doesn't drive and sent her kid over to pick them up.
Person 2: Yeah, she's probably a fat shut-in.
Person 2: Yeah, she's probably a fat shut-in.
by William J J T October 29, 2010