Tub is a passive man and is the brunt of many jokes; to cope, he overeats and is fat. He lies about his weight, saying it is the result of a gland problem, but in truth his fat allows him a personal excuse to continue accepting the abuse of others.
"Always having to think about what you say and do. Always feeling like people are watching you, trying to catch you at something. Never able to just be yourself."
(Wolff, "Hunters in the Snow," classicshorts.com)
Consciously, Tub eats to escape and to give himself some small pleasure that others can't steal from him. Unconsciously, he thinks that if he has some specific fault -- in this case, obesity -- that others may pick up on, it excuses them from their cruelty and makes the jokes less painful. Tub thinks that as long as he can attribute all the jokes to his obesity, then they are not directed at himself personally.
He is insulated from life by his layers of fat just as he is insulated from the cold.