I like reading your questions.

I do think you're onto something. I think it's referred to as "mirroring" when we complain or dislike traits in others that we subconsciously see in ourselves.

I also think it's circumstantial. For example, an optimistic person may be more sensitive or aware of a pessimistic's behaviour because they're not inclined to operate in such a negative way themselves that it stands out. For example, I rarely swear and dislike it when people swear during casual conversation so when they do, I notice and it makes me uncomfortable (for a moment).

I've definitely been in situations that I've disliked, only to realize I, too, behaved in that same way. So I think it's important to ask yourself, why does said behaviour bother you so much?

Self-reflection is only self-reflection if you're able to self-reflect.. or else it's just blame, projection, or denial.