Oh, hey, I almost didn't recognize you outside of work.
A joke about "Moby Dick." In the story, the one-legged protagonist is a sailor ruthlessly chasing down the whale who ate his leg. The joke is that both the whale and the sailor only did these acts as a job, and that off the clock, they casually ran into each-other at the grocery store. While work colleagues not recognizing each-other outside of the office is a common occurrence, it's surprising that the obsessive sailor has disconnected from his work enough to not even recognize his biggest rival in life.