I'm not sure which cinematic trope you're actually trying to emulate, the versions I generally see are:
- Someone does something that reveals they're a badass. Observers go 'OMG, that guy is more dangerous than we thought', and depending on the situation, might need to make a fright check or be more vulnerable to intimidate. This doesn't require special rules.
- Anime-style 'killing intent' or similar, which doesn't generally require any specific action.