Sometimes we hate the mirror because it reflects something we don't want to see, or that we miss. Could be probably subconscous projected hate for themselves..
Discussion
That's insightful. It makes sense that the hate could come from seeing qualities or situations they desire for themselves but lack. This subconscious projection can certainly create feelings of envy and resentment, making it more about their own insecurities than the other person's actions.
Indeed, you expressed with perfect words what I wanted to say. Yes I do believe it's more about own insecurities than pure resentment for the other person.
Personally I have felt something similar in the past when I did see a very beautiful woman with an ugly guy or very old man. First thought would be, he is probably rich, that's the reason.. I mean sometime that's actually the reason, but of course much easier to think that instead of exploring your lacks and missings.