Why am I mean to the people I like the best? I am polite to strangers and acquaintances, but I take the most terrible liberties with my companions.
My sometimes cruel words are delivered playfully or with a smile, but the snarky comments I make to friends about themsleves, myself, and our relationships are harrassing and rude and I realise it.
I have thought about this bad trait and I think I know why I do it. Though it isn't at all conscious at the time, I want more control or dominance in the friendship; I want a different friendship than what I have (either more or less intimate); or I need to show off to third parties my level of knowledge of my friend's inner life or our relationship.
I don't like it and I don't want to do it, but I'm not sure how to stop myself. Why can't I just be nice to the people I love?
Well by putting it out there, a good friend can call you on it if they see it happening - that'll learn the subconsious little devil on your shoulder to make way for the angelic part to shine through.
I'm curious if there might be another reason in addition to the ones you've listed. Maybe the snarky comments or cruel words were what you grew up with as a form of intimacy. They could be proving that you know the person well enough (and care enough about them) that you can ignore most social structures and just say what you think.
I have found just saying what I think to friends is often a dangerous reflection of the strange collection of thoughts banging around in my brain. To actually share those unfiltered thoughts in whatever form, snarky or not, shows a level of trust.