What do you when someone interrupt while you're talking?

Philippines
November 11, 2009 6:01am CST
For me it's quite rude when someone interrupt while you're talking, it annoys me sometimes especially when the person is not really close to me, and I'm discussing very important thing. But when someone interrupt by just saying hi or hello then I don't mind, but participating or worse diverting the discussions gets into my head. What do you do when someone interrupt while you're talking? Do you tolerate that kind of behavior?