|If someone puts you down, just tell them, "That's your opinion," because that's all it is, and both of you should realize that. ~Doe Zantamata|
But the truth is different for each person. If someone's gone so far as to insult you, they've already formed an opinion, and it's likely much different than what you know to be true of yourself.
One person should not have the power over you to really ruin your mood over something that's not true anyway. But it's up to you if you'll give it to them or not.
If you get mad, try to explain, or try to prove to them in a few words the opposite of what they've just said, they'll likely keep going and get even meaner. So why bother?
Refuse to accept their opinion as your truth.
Don't bother arguing.
By saying, "That's your opinion," you're allowing them to have their (ridiculous) opinion and showing them respect, but not accepting what they've said as your truth.
Maybe eventually they'll wise up and see that their insult was misdirected, unwarranted, and just plain mean, but if they do or don't, it's not worth spending a second of your precious life worrying about it. You've got way better things to do.
By Doe Zantamata