It is a case by case thing. In my case my H dissociates - so it is like he is "possessed" and in a different mindset. It is a bit hard to explain. You could read through some of my old posts to get a sense. I actually have a list of "tip offs" about how to tell he has gone "into and episode" and is not just tired and grumpy. For him, there are key phrases that tip me off "I will not be disrespected" "I'm always wrong." that sort of thing. Also he acts differently, his manners go on holiday, no please or thank you. He cannot take in new information. I can tell from his general demeanor - his face and general stance - that he is probably "gone."
But this may or may not be helpful since not everyone with PTSD dissociates.
We tend to center our understanding around the dissociative episodes, so the other stuff is in the category of "lead up". So for instance, we recognize that crowding will trigger anxiety and irritable behavior. People being harsh with children, or animals will do the same thing. Honestly, the list goes on.
The response at the moment is much the same whether it is PTSD or being a jerk; set good boundaries, do your best to figure out how to de-escalate. And then, talk about it later when they are calm. If they won't talk or take action to correct the behavior - it doesn't matter whether it is PTSD or not IMHO - its not workable and the relationship has crossed the line into abuse.
I'm no expert. But that's my take, for what its worth.