"You're Overreacting" what this means when a narcissist says it

 It's emotional manipulation and a way to devalue you. It's also a "great" way to tell you your response to their shocking behavior is not valid. A narcissist expects/demands freedom without consequences to say/do whatever they feel inclined to while telling you you're overreacting when they do/say the most jaw-dropping, immoral/questionable things to you.

Is it fair? Of course not, but you have to expect it from a narcissist. 

If you're dealing with abuse, talk to someone or get professional health. Your scrambled brains will thank you.