Some people do not even notice it when they're interrupting others.
When someone talks while I am talking, I just try to make him/her understand that I don't wanna be interrupted by raising my voice.
Or I also stare at the person with a neutral look, but this doesn't mean I appreciate this behavior.
When people interrupt me, I think they don't care about what I'm talking about or what I'm doing, or anything else, so, I do just as they do, I show them that I don't really care about the thing they wanted to tell me, but if it's important enough.