There are cases and places in which I feel justified in interrupting. Primarily, at work and often in meetings there.

For instance, if the person speaking hasn't got to the point in the first two sentences, I will gently encourage them to get the Hell on with it. Similarly, if they have failed to say everything they need to say about their topic within five minutes, I will enquire as to whether they've actually thought it through or not.

To avoid interruption myself, I speak to the point, only to the point, and make sure I've honed down what I need to say to the shortest time possible. Again, if I can't get it down to five minutes, it's because I myself don't understand it properly, so I don't talk about it until I do.

As I say, that's at work where one should be spending time doing things, not talking about them. Outside that context, I don't interrupt people. Don't say much, either. I have two ears and one mouth, so I try to listen twice as much as I talk. Besides, as a Bear of Very Little Brain, I don't have a lot to say.