Argh... we have our moments of frustration, but that's all they are, frustration.
I learnt that when in such situations to put myself in their position... thinking about it often resulted in the person being stuffed around is likely just as frustrated as we with PTSD are watching, waiting... but if they don't have PTSD then they don't show it like we do... usually resulting in anger, so I use them as a learning mechanism of what I should strive for with patience and understanding, ie. things happen outside our control, then shit just happens sometimes.
I use the same with driving, ie. the person in a hurry who just cut me off or such, well, I could get out and put my fist through their window, or maybe they have PTSD also and feel the same as I do! Interesting thought...