A very easy, low friction way to correct this behavior is to steer the conversation to someone who has been interrupted.

Let the interrupter do his thing, then go "Alright John Doe, you were saying X Y Z?" He'll start his train of thought again, and if someone tries to interrupt, cut them off and say "Hold on let John Doe finish answering my question". You come out looking professional to interrupters, the interrupted likes you more, _and_ you start to change the behavior that annoys you, without you being the bad guy. win-win-win