Harley Quinn: Huh? What was that? I should kill everyone and escape? Sorry. The voices. Ahaha, I'm kidding! Jeez! That's not what they really said.
The Joker: Would you die for me?
Harley Quinn: Yes.
The Joker: No, no, no. That's too easy... Would you live for me?
The Joker: What do we have here?
Harley Quinn: What you gonna do? You gonna kill me, Mr. J?
The Joker: What? Oh, I'm not gonna kill you. I'm just gonna hurt you. Really, really bad.
Harley Quinn: You think so? Well, I can take it.
Amanda Waller: She was assigned to the clown himself. She thought she was curing him, but she was falling in love.
Captain Boomerang: You know what they say about the crazy ones...
Harley Quinn: Huh?
Rick Flagg: This is the deal: You disobey me, you die. You try to escape, you die. You irritate or vex me... And guess what? You die.
Harley Quinn: I'm known for being quite vexing. I'm just forewarning you.
Answer: Because he's already been into the liquid, it's how he became the Joker. He wanted Harley to be just like him.