I love helping people and all but I also set boundaries. I'm only kind to those who are kind to me back. I am kindhearted until you get on my BAD side. Don't push my limit. If you do I'm done.
I'm a nice person until you make it known that you feel you can shit on my head and expect me to take it. Then the usual response is, "Wow, you were so nice. Why you gotta be such an asshole?" Translation: "Hey, I thought I could use you as a doormat, now you have a pistol in my face. Boo!"