Croesus
Adventurer
I don't understand why PCs would trash-talk vastly more powerful NPCs unless they think the GM won't punish them.
Well, by design, the game does put the spotlight on the PCs. So sometimes players forget to treat NPCs as anything more than props. That's when the GM needs to remind them, which I did. It definitely took the players completely by surprise, and they haven't repeated that particular mistake since.
Another reason could be that sometimes players just aren't invested in a serious session. For whatever reasons, they just want to consume munchies and make Monty Python jokes. A GM just has to roll with it at times.