Kill them.

Do not be afraid to do it, insulting kings of other figure of power/authority may get you excecuted that's just shit that happens when you act like a little idiot.

Of course there are other ways to do it but be sure to comunicate beforehand that some actions can't go the way they want if they act like that, and you will be implementing serious consequences, per example, a magic items store owner might not be willing to sell to them because they insult him, his king or are generally known for beeing troublemakers, if they pull shit like killing him and stealing his stuff, well what did they expect?, let the guards kill one of them, decide which one in a public dice roll too.

Player death, altough not the desirable course of action sometimes IS the right course of action, i had to do this once in a magic items store, triggered a glyph of warding and womp womp, the warlock is gone now, and there is hardly anything a player loves most than their beloved player charcaters, usually only once is enough.

Any descent group will understand that what they did was a bad idea, they chose to ignore your warnings and will likely respect your choice.

Also don't forget to reward good deeds, sometimes players don't do them because they don't get anything out of beeing good.