F*ck being nice to everyone.
If someone treats you badly, you have every right not to tolerate that bullshit.
The way people treat you is a statement about who they are as a human being. It's not a statement about you. So if you put an end to their bad treatment it's a statement to them that you're not here for their bullshit.
You're not required to set yourself on fire to keep other people warm. Remember that.