10 Problems With The Joker Nobody Wants To Admit
5. He Isn't Funny

Inconsistent though The Joker's various characterisations have been, they usually all fall back on a particular core thing that he wants: to make people laugh. Or, to make himself laugh. Or to make the usually stoic Batman laugh that's the ultimate goal.
Anyway, what The Joker wants desperately, more than anything, is laughs. He's like a deranged Michael McIntyre. Perhaps a little less horrifying. And at least he's fictional. The Clown Prince Of Crime enjoys causing chaos, and trouble, but usually it's all in pursuit of one huge joke, a punchline that is sometimes not so literal...but sometimes is. But here's the rub: The Joker isn't funny. How often have you seen him crack an actual gag in a comic, film, TV or game appearance and actually chuckled? Probably never.
The dude just isn't funny. Perhaps that's why he had to give up the stand up comedy game (if The Killing Joke is to be believed) and get into crime instead. The other gig simply wasn't working out. Regardless, having a character whose whole shtick is based on him being at least semi-humorous and then not having him actually be able to make people laugh? That's bad.
That's what people in the industry call a Deadpool.