When some one who is so fat runs an mile they start to sweat lard, grease, and cooking oil.
The sweating of these materials can also happening by other extreme workouts. Usually excretes as ass sweat
Timmy: What happened to Bruce?
Billy: He ran a mile and now he's got a bad case of the "lard ass"
Bruce:(Sitting in a puddle of lard, grease, and cooking oil) Hakjwbdwebfawieubciawrfiwqciubudisclijcv9upgvpurvprvub
Timmy: What a lard ass.