He was resentful of his hand and the negative attention he received because of it. He wrote a message on it to confront his coworkers: "I am tired of these jokes about my giant hand. The first such incident occurred in 1956 when..." before cutting off.[1]
He later explained that his hand's large size was due to exposure to the radiation in the Plant's reactor core and encouraged Homer to put a donut in the reactor core to make it bigger.[2]
Although it was his most striking external feature, he nonetheless sometimes seemed to forget which of his hands was larger and was therefore surprised when he accidentally held it up to show his colleagues. His hand appeared to be heavy enough to cause him to fall.[2]
When the alarm at the Nuclear Power Plant was deactivated, several employees complained about the sudden silence. The guy with the big hand told them to be quiet.[3]
Episode – "The Last Temptation of Homer" 
Comic story – Simpsons Comics 133 (cover)