Odo the Bar Shape-shifter in the Alleyway Scene from Star Trek

Listen here, you soft-brained chucklehead, this is a play on Odo's shapeshifting ability from Star Trek: Deep Space Nine. Odo is a Changeling, meaning he can change into any form he wants. So, when the joke says he "turns into a bar," it's not just him walking into a bar, but literally becoming one.