It took a few minutes for me to put together why I had such a visceral response to something that most people would see as neutral.

Probably a decent rule of thumb for identifying when someone is triggered … when their behaviour is suddenly and inexplicably extraordinary to the point that they don’t even know what happened (and probably really don’t want to talk about it)

Which if true (I don’t think I have nearly enough experience here) might be a helpful framing so that whenever something like this happens, and it isn’t a repeated asshole behaviour or something, you know that you’ve got someone dealing with trauma and can help and accommodate accordingly.