Just the derpy screams and noises they make when you try to talk to them, bump into them, or threaten to hurt them. The acting of the inconsequential NPCs in general felt really aggressively bad to me. From the perspective of someone who doesn't play these types of games, it's just this weird mix of the campiest of camp combined with storytelling that seems to try to be more serious and pristine. I don't know if it's meant to be an intentional attempt at humor, or what, but I'm not into it.
Again, I'm under the impression that this kind of thing is super common and gets memed on a lot in things like Oblivion and Skyrim, but going into it, I was hoping that it'd be something that The Witcher 3 transcended (since it has this critically flawless reputation), and it was still pretty bad for me, personally.
For the record, I only started the very beginning of it (and I assume that more story-relevant NPCs are better), so if it's some intentional reference or rug-pull that doesn't persist throughout the game, then I stand corrected.