Comebacks to use when a guy mansplains to you.

-What makes you think I don’t know this? 
This response challenges their underlying assumption that you know less than them, asserting your competence and knowledge. It also lets the person know that their unwanted explanation is unwelcome and establishes a boundary against future similar behavior. It’s important that the delivery is said in a calm, confident, and direct delivery to ensure it comes off assertive. Be mindful if delivered with anger or hostility it’ll come off as passive aggressive and could escalate the situation. 

-I’m comfortable with my understanding, thank you though. 
This phrase is direct and clear, leaving no room for misinterpretation and avoids attacking the other person and is polite and assertive. It also sets a boundary that you’re not open to further explanation on this topic. And it preserves self-respect and confidence by asserting your knowledge and autonomy without escalating the situation and maintaining control of the conversation. 

-Please respect my knowledge and experience on the topic. 
This response is assertive, direct, and clearly states that you have knowledge and experience on the topic and that you should be respected. By asserting your expertise and authority it challenges their underlying assumption that you’re less knowledgeable. If conveyed in a firm and direct tone you can effectively establish a clear boundary that their behavior is not acceptable and discourage future instances of  mansplaining.