The act performed by males to temporarily increase the appearance in size of their genitalia by tugging or groping their groin to induce a "chubby." Often performed in a locker room when concealment of a shower stall or towel is provided.
The chub tug can also be performed prior to public exposure of genitalia for things like medical examinations, streaking, or skinny dipping.
Meat gazer 1: Did you see that guys 2 inch schlong in the locker room?
Meat gazer 2: Ya, normally it's about 1 inch but I saw him do a chub tug under his towel a minute ago.