One of the biggest annoyances for most people is when someone close to them makes a comment or judgment about them like they really know the inner workings of the person in question. We try to decipher the reasons behind this phenomenon.
They may know the real you
Unless the person behaving like they know the real you is just an acquaintance or a total stranger, a person who acts like they know the “real you” may actually know the real you. You may not actually agree with what the person has to say but that doesn’t mean that the person making the comment is making things up or making an assumption.
Your perception of yourself may differ with your projection of yourself
A lot of people have a very different view of what they are and what they think they are projecting to the world. Hence, when another person makes a comment based on your projection of yourself they are in fact rather justified in assuming they know the real you even if you disagree completely with it.
People can only know you based on what you show them
Someone can know you based on two things- a) what you tell them about yourself, and b) what kinds of behavior you have shown them over the years. Unless you actually tell people about your personality yourself, they will only have your behavior in the past to work with and to make judgments about the “real you”.
if their assumptions about you differ from your own view of yourself, you may have to either offer clarifications to correct their assumptions or learn to let of such annoyances and be happy with the knowledge that they are making educated guesses and that they don’t in fact know the real you.