It depends on the person. Some people may talk more and ramble because they're triggered and uncomfortable. Others freeze up and go distant. Certain people may excuse themselves from the situation and run away, hiding away until they feel safe again.
Often times, people can mistake a person being triggered as an anxiety attack, when it isn't quite the same thing, and a person with PTSD may not be showing any visible signs on the surface like shaking or struggling to breathe while experiencing great inner turmoil, nausea, and adrenaline rushes, a sense of feeling violated. It varies a lot from person to person.
My PTSD can make me dissociate heavily and freeze up, being unable to stand up for myself and fight back to evade triggering situations. There have been many occasions where I was suffering from PTSD and experiencing great fear because I was in a medical environment, and the staff could tell that something was wrong and my body was stressed out because I needed them to desperately back off and quit touching me, but they would laugh at me and say I was being an anxious little girl even though my blood pressure was through the roof.
Even when I have explained that I have PTSD to many people, they seem to think it is like the anxiety someone may feel before giving a presentation, or mustering up the courage to go speak to a cashier if you're socially awkward, which eventually fades once you get through the stressful situation. They don't realize the body and mind get to replay feeling violated over and over again, or that your body gets flooded with stress hormones indefinitely each time this happens, because they can't see it with the naked eye.
And even things that may not trigger you anymore can have lasting consequences on mannerisms and behaviour if you have been conditioned by abuse. Often times people don't realize that is a consequence of a traumatic childhood or adult relationships.