Mr. Joker, you say such beautiful things. Oh, you're so powerful. And purple! Oh, I love purple.

"Did you ever dance with the devil in the pale moonlight"?

---

If you did, did you look him in the eye?
Did you dance the poison out of your soul,
and dance the devil back into his hole?
Well, you better say never,
because the dance with the devil might last you forever.

 Alex Ross, Tango with Evil - The Joker and Harley Quinn, 2003.

urbandictionary

 Line habitually used by the Joker (Jack Nicholson) in Tim Burton's Batman. Have you ever danced with the devil in the pale moonlight? I ask that of all my prey. I just like the sound of it.

 imdb

 Vicki Vale: [distracting Joker] Mr. Joker, you say such beautiful things. Oh, you're so powerful. And purple! Oh, I love purple.
Batman: Excuse me.
[Joker looks]
Batman: Have you ever danced with the devil in the pale moonlight?
[punches him]