The Do's and Don't's of Agreeable Conversation : Page 182

But if anyone ever interrupts you in this irrelevant manner; remember that you are talking not to please yourself but others. Whatever you do, do not allude to the interruption. Pretend not to have noticed it and glide with the others into the new topic. If the guilty one directly offers you an apology, and requests you to continue what you were saying, accept the apology gracefully and as unobtrusively as you possibly can, and do continue what you were saying. However, it is well to recognize in the interruption a hint that your theme was not of sufficient or general interest and therefore do shorten it gracefully, if possible concluding it with an opening for the topic which constituted the interruption.