I think it comes from "blousing strap" that keep your pants from coming out of your boots in the military. Im sure you can work that into a fatty coming out of her too small clothes.
"Check out that blouser! I wonder which way is front..."
"That kid Matt is such a blouser".
This occurs in a discreet manner as possible. When the situation arises knowing looks are exchanged between friends and colleagues who them also share in the blousing.
Individuals who excel in this activity are referred to as "King Blouse"
"Yeah he's the King Blouse alright, I don't know how he gets away with it........"