I was a bit happy a few days ago. It all came crashing down yesterday. Why do I let peoples opinion of me bother me?

and it wasnt even because it was one of those days or M said something.

It takes some years on the neck (as we say here) to learn self distance from those who serves you no good purpose. As in disengage and mute /block people.

In the end the last opinions we all care about. Are what we ourselves think about us.

Because you're human and not a cat, be more like a cat.

All joking aside it can be hard not to let other peoples opinions affect you but unless this person is somehow terribly important to you why care about a random opinion?

I don't know but could be because a part of you agrees with them. If it didn't you'd just laugh in their face.