It's a new template. Instead of "Bad Pun Dog," it's "I'm Bad at Puns Dog."
The joke is that he gets the joke wrong. He was supposed to say "Two goldfish are sitting in a tank" to build up to his joke, but he said "Two goldfish are sitting in an aquarium," and ruined it for himself. Do you see it? :)
It's a new template I'm trying to get started. :)