I've been teaching for about 10 years now and one habit I can't break is cutting off the students before they complete an answer. I don't always do it but sometimes..... It is not malicious, but often the students answer will set off a new idea for me and I'm asking a followup or discussing the idea before the student finishes. I have tried to break the habit but without success. I often find myself at break time talking to the student and making amends. One of these days I'll figure out how to stop without forcing those long pauses where you then realize they actually were done 20 seconds ago.