It's Batman, Batman and the Brain

While watching The New Batman Adventures S1E10 with my son, I was amused by this exchange:

Batman:
What are you doing tonight?

Barbara Gordon / Batgirl (dramatically):
The same thing we do every night, Pinky.

Batman:
What?

Barbara:
Never mind.

My son has never seen Pinky and the Brain, so it was lost on him.