From an undated but late Victorian self-help / etiquette book called Don't: A Manual of Mistakes and Improprieties more or less prevalent in Conduct & Speech (Ward, Lock, London circa 1900). The author is noted as 'Censor' and some of the advice still holds, e.g. bores, exaggeration etc., as for the 'scandals of the hour' - it would now be considered very dull NOT to be able to discuss them...more to follow.
DON'T talk over-loud, trying to monopolise the conversation.
DON'T talk to one person across another.
DON'T whisper in company. If what you have to say cannot be spoken aloud, reserve it for a suitable occasion.