Question

Why does Andy call Jim “Big Tuna”?

Answer 1

In The Office, Andy Bernard calls Jim Halpert "Big Tuna" as a reference to a prank Jim pulled on Andy in the episode "The Duel". In the prank, Jim placed a large tuna in Andy's office, which Andy believed to be an actual fish. Andy then began to call Jim "Big Tuna" as a nickname in retaliation.

Answer 2

Andy calls Jim "Big Tuna" because of a joke he heard from Jim's predecessor, Tom. Tom once jokingly called Jim "Big Tuna" because he had a tuna sandwich for lunch. Andy thought it was hilarious and continued to call Jim by that name, despite Jim's protests. It became a running joke between the two characters on the television show "The Office".