Way I see it if he conforms to a single mode of style of speech he loses that sense of a chaotic mind to him. The fact that it got you out of nowhere strengthens that this cursing that's out of character is in character. Meaning that Joker being out of character is him actually being in character to an extent.
This. I have studied Joker extensively in the last couple of years and I have come to this conclusion about him. True, it's really just different writers giving different interpretations of him, but the changes have been so drastic that it became a character trait in and of itself.
@CadenceV2: I know, but I felt it worth pointing out every detail. I was originally going to also point out that using scans from the 60s for this debate was kind of pointless when Erik has done far more impressive things. Believe me, friend, I've got scan upon scan for Magneto. He's among my top favorite comic book characters of all time. Heck, my original user name on here was "Ultimate Magneto" (though make no mistake; I dislike the Ultimate universe.)
@TheSecondOpinion: I know, but he mentions giving them "another demonstration of [his] power," then monologues how he is using that device in this second demonstration. Plus this isn't out of character since he has used power boosting devices in many other stories.
What I'm about to say is not a definite, just a theory. Because of Mark Hamill's portrayal in the animated stories and animated movies, Joker cussing seems out of character since he never cussed in those instances. I can't even recall when Joker cursed in Tim Burton's or Nolan's flicks. Then again, lots of things don't get said or shown in a cartoon. Like people having intercourse, cussing, and gory violence - things we know happen in the real world. Like I said, this is more a theory than anything else, but it could just be nostalgia from the animated series that's making his cussing seem odd to you. What do you think?
If it's purely fisticuffs, Joker takes it. If it's who is funnier or crazier, then Joker takes it. Lex Luthor for pretty much absolutely everything else. Joker's smart, clever, and can come up with great plans, but Luthor is honestly better and has far superior resources too.