There are ways. You could, for example, set up a bbeg where that’s his whole deal. The townsfolk are scared of this guy because he has the supernatural power to just kill you, straight-up. Maybe the questline leading up to their encounter involves the players finding defenses or counters or sabotaging his supply of spell components or whatever, such that, if they DO get power-word-killed, it’s because they had ample opportunities to not, and failed to take them.
He even did the full chest bump thing. And then in case there was any doubt, he did the whole gesture again.