What you describe (someone's button's being pushed) is commonly known as a trigger. What they are experiencing might even be related to PTSD, though probably not in your example with the misplaced comb.

Yeah, I have tried to keep in mind that there might be some time in my friend's past where it was useful for him to freak out like that.

This may work in isolated cases, but most of the overreaction you describe is subconscious. Logic does not work well on the subconscious mind, if at all.

I think this is a little too simplistic. You can bring things to the level of someone's attention that wouldn't have been noticed without guidance, and by repeatedly relating immediate contexts to previous contexts that included rational arguments, people can learn how to do new things just like they have their entire lives. The fact that we call them rationality techniques doesn't make them different from all other skills in any special way. They're just metacognitive skills in particular.

This often comes across as condescending and may easily cause resentment.

I don't use that word when I'm talking to someone. I did think, after the fact, that all of this talk of 'instilling behaviors' and 'teaching' would sound a little too Orwellian, but hopefully everyone can see that this is not that, and that this is not very different from how people manage social expectations all of the time. You're just explicitly optimizing them now.