gerunds - What is the grammar of: "You being the fish"?

Source: The Big Bang Theory transcript season 2, episode 1

I found it weird when I heard it in a tv series. 'Being' is not preceded by a 'to be verb' and also comes after a subject.

How is it possible? Shouldn't it be "You are being a fish"?

Leonard: Okay, so, she said she wants to slow things down. It’s like saying “I’m really enjoying this meal, I’m going to slow down and savour it.”
Howard: No, it’s like “this fish tastes bad, so I’m going to slow down and spit it out.”
Raj: You being the fish.
Leonard: I'm not the fish.