I've not seen the film, but it does sound like ego tripping which isn't abnormal. I think it's difficult being an actor. Way more difficult than most people realize, but it is possible (speculating) that Jared Leto tried too hard.
Many great actors have fallen into the trap of overplaying, when portraying a psychopath characters. Why? Because playing crazy loonies is the favorite thing for actors. They get to be broad, express themselves, and are much more unhinged than playing good characters.
And there is something the audience picks up about an actor playing "crazy". Much like actors being drunk. It's very hard to pull off. The audience gets annoyed quickly because it robs the story of having to make sense. Having a psycho character means that the character can break the dramatically based structure and not adhere to the script. It doesn't have to make sense because the character is insane, and so the actor can do what it wants, acting like a baby. It gets old.
So to pull it off, an actor/actress need to find a very narrow window of being insane, and being coherent and relateable in some form, and Heath Ledgers Joker did that. Ledgers Joker, like Nickelson also absolutely nailed the one-liners ("why so serious?", "some men want to watch the world burn" and so on) and that was incredible entertaining.
I don't understand it because Jared Leto is a great actor, but he also has an ego. He won an Oscar even. He doesn't have to be so upset.