You have something important you think to say in a group of people .You start off to relate the story and one by one "audience" just start to do something else or start talking amongst them selves do you A continue on hope they are listening although it dont look like it B .Stop talking and join in in their conversation C Storm out of the mumbling "nobody listens to a ...word I say and slam the door" .Which are you? .Me Im the door slammer.
It's not happened to me before but if it did then I would assume that what I've got to say might only be interesting to me and join in with the rest of the conversation. I certainly wouldn't throw a childish hissy fit ala your option C.
I drift off and fall asleep when I am talking......actually I have seen this done, when an economics lecturer fell asleep, sitting on the desk, as a conversation cascaded around a hall of 100 folk.
It depends on your 'audience'... if I'm chatting in a group of friends then conversations go all over the place, plus I don't think a group of friends chatting constitutes an 'audience'! If I'm giving a presentation/training a group of people then I make it as interesting and as relevant to their jobs as possible.
Another thing that annoys .You are having a conversation with some one .Their phone rings they answer it and leave you standing there .Do you walk off .wait till they are finished .or .....Not every call is of great interest to the whole of society .Would the proper thing to do it excuse themselves and tell the caller they are in conversation and unless its very important could the call sometime tomorrow