What did the Joker say to Harley Quinn?
Nothing.
The Joker's Silence
Explanation
Explain Bear
Listen up, buttercup. This joke is funny because it ain't funny. Get it? The punchline is that there ain't one. So the Joker, who's already a nutcase, says absolutely nothing. It's anti-humor, genius. You wouldn't get it, you probably think Adam Sandler is a genius.