@jarkko it can be really difficult to find the right level to respond with sometimes.
I think the key thing is to try always to be as civil as possible, even if the person is being an arsehole. Sometimes you do need I think to push back and to be firm, but maintaining the civility not only keeps things professional and takes into account that we're all humans, but in addition allows you to row back reasonably from a mistake in case you were simply wrong/misunderstood (important to do that if you have too!)
I think in cases where somebody is doing something that would be harmful to the kernel it's important to be firm (and NAK as necessary), but again to remain civil.
But we are all human and all make mistakes in this arena. Of course a CoC codifies a baseline of acceptable conduct but I think you have to hold yourself to a higher standard as much as you can.
I think sometimes when you find you have a very emotional reaction the best thing to do is to sleep on it or take a walk and calm down before responding, or draft a response and re-read in the morning/etc.
The general thing I always try to maintain is - I would say anything I say online in text form to somebody in person face-to-face.
I think text is a shitty medium of communication and absolutely language and especially cultural differences (some cultures having a more 'direct' style vs. others for instance, or some being more abbreviated that in other cultures would be considered rude etc.) can play a role in misunderstanding.
I think it's unavoidable so just has to be managed as much as possible.