Keeping the Crazy out

Why are people so determined to bring you into the crazy??? I don't know if other people experience this problem but it feels like I am constantly being asked to participate in crazy. Today I agreed to go shopping with my future roommate because she needs to get some items for her sons for the move. Unfortunately we had to stop by to drop off her son for his nap at her house (which she is vacating) and her crazy partner came out to freak out at me. She is mad because I refuse to communicate with her. Why should that be a problem? I am not refusing to communicate with her about the children but I am refusing to communicate with her outside of the children. Why should I be subject to such intense craziness? I do not need this in my life and am trying to create a boundary. This should not be so hard but yet every time I try to place one I receive resistance. I do not want crazy people in my life, that is why I am no longer communicating with my Stepmother. I do not want hurtful people in my life. I do not want people who drain me of all emotion. I do not want people who do not bring anything positive to the relationship. Is this such a huge line in the sand? Apparently so.