[Ulzgoroth]

I'd invoke Tactical Shooting's Threat Recognition rules (p33). Though yeah, for detecting threat signals from the social situation rather than the tactical situation would draw on different skills.

Notably, even action heroes and superheroes may not live up to the constant vigilance that that book accords to anyone with Combat Reflexes.

I'd probably require a successful Acting roll to not tip your hand to someone that you're socially interacting with about your intent to attack them. Not a contest. And if somebody successfully uses Body Language that would also give warning.