So many people fall in the trap of not speaking up when something somebody does upsets them, then because they didn't say anything the person continues to do it. Why would they stop doing whatever 'thing' is when it clearly doesn't bother you?

It always ends with an enormous 'Straw that broke the camels back' blow up where the other person is absolutely blindsided by the intensity of your response because they never knew it bothered you - how could they?

If something upsets you - speak up there and then, or shortly afterwards in private. If it doesn't bother you enough to speak up then you need to let it go because it's not fair on the other person to keep letting them upset you when they don't even know they're upsetting you until you blow up on them.

I think people sometimes don't think about how much it can suck to be on the other side of this too - interacting with a friend and doing something you thought was completely harmless only to find out after months that all this time you've been really hurting them the whole time and didn't know.