[Celjabba]

Social Engineering p68-69 have rules for Intimidation bonus and malus, including the effect of SM :
Add the SM of the person making the threat, and subtract the SM of the target.

You may also want to look at raising will, or at the talent Though Guy or Mr Smash.
Appearance(impressive) or going the other way, hideous or monstrous is also worth a bonus
perhaps also the perk controllable disadvantage : callous

Conan in a tavern would benefit from
*18 in Will (according to Gurps Conan),
*+2 from charisma
*a +1 for SM,
*at least a +1 for just being obviously strong, possibly up to +4 if he display his strength menacingly,
*possibly a complimentary bonus using streetwise to know how to handle this specific rough crowd,
*probably a bonus from reputation or even social stigma ("It’s not wise to upset a Wookiee"),
*possibly a bonus from talent.