This sounds stupid but he is unironically the closest real life person I can think of that matches the Joker. His goal is that he has no goal, he does what he wants under some pretense that it's about getting fair treatment, autism awareness, a diagnosis, etc. He does what he does because he enjoys it, he gets off on it. There is no further goal beyond that, there never was. It's just he traded blowing up hospitals and being a crime lord for smearing his crap on windows and throwing a tantrum at his aging parents and brother. Still just as distressing though.
“I’m like a dog chasing cars, I wouldn’t know what to do if I caught one, you know, I just do…things.”