pathological interrupter

When you are expressing an important concept or imparting an important situation, the pathological interrupter will change topics in mid-sentence as you are speaking. They continue to do it after you call them on it because they are insecure in themselves and don't realize they are doing it.

I was telling them a story about how the neighbors were robbed at gunpoint and the pathological interrupter started speaking about his greatness at his job and how important he is there.