As we reach different points in our lives, we have people that we were friends at one point but now you no longer wish to have that friendship because you have learned and grown and realized that this person is full of negativity, or uses others to benefit themselves, etc

How do you cut off these people out of your life?

This person in particular is a high school classmate. We were close at a certain point but no longer. This person is clingy and pushy and does not respect boundaries. This person has shown up at my house without calling, calls my sister to ask what is wrong with me and am pretty sure has talked to other mutual friends about me. I just don't want to be bothered with this person, period. I am cordial, respectful but I keep my distance. I don't feel like I owe her or anyone else an explanation for my behavior.

Has anyone else dealt with someone like this and if so, what did you do?