I think you know what's meant by "It" in the post title. You would think that this happens more often at work than in the family, but it can happen anywhere. You are the victim of someone's bad mood, but instead of making things worse for yourself by snapping back at the perpetrator, which would only cause you more problems, you pass it on down to someone else who can't fight back. Remember this comic from Lunarbaboon the next time you are tempted to take it out on someone.