All the time. My sister was the first one to tell me I do it when I was about 19, since then lecturers, bosses, friends have all told me to stop doing it. So now I know I do it, but have no idea how to stop. If I pay careful attention to whether the other person has finished, I never get a chance and end up saying nothing, and it's such hard work, especially in a group.
Has anyone figured this out? Can someone teach me how to have a conversation without annoying people with interrupting?