system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] What is the relationship between Lex Luthor and the Joker?

In theory, there should be no relationship whatsoever between a megalomaniac multi-billionaire genius from Metropolis and a crazed multi-murderous criminal from Gotham.

But of course in the comics the community of villains is a big community where everybody knows everybody, hangs out in the same bars, plays poker in the evenings and gives each other birthday wishes. And the nemeses of the world's finest heroes are bound to have crossed paths several times.

So, what is the relationship between the Joker and Luthor? Do they respect each other? Do they detest each other? Does the clown find it funny to tease the serious criminal mastermind? Does the billionaire find it necessary to include the Arkham Hotel's most loyal client in his plans?
gpt
Neither Lex nor Joker could ever have a real friend. But they do see each other as colleagues and they’ve teamed up a bunch of times (I dunno, probably like half a dozen at least in the Silver Age). 

Lex knows enough about the Joker to always involve him in big plans (because he’ll get offended to learn he was skipped over), and they even tag teamed Lex’s awful son this one time.