“Be who you are and say what you feel, because those who mind don't matter, and those who matter don't mind.”

This was written by Bernard M. Baruch

Now what does it mean?

Meaning

Be yourself, if they chose not to respect you, you could choose to find someone that does. There are 8 billion people in this world. You deserve to find someone who does.

Plus, the wasted energy from not being yourself is way to annoying to bear.