3. Never interrupt anyone who is speaking; it is quite rude to officiously supply a name or date about which another hesitates, unless you are asked to do so. Another gross breach of etiquette is to anticipate the point of a story which another person is reciting, or to take it from his lips to finish it in your own language. Some persons plead as an excuse for this breach of etiquette, that the reciter was spoiling a good story by a bad manner, but this does not mend the matter. It is surely rude to give a man to understand that you do not consider him capable of finishing an anecdote that he has commenced.
I have been interrupted in conversation before and it's depressing and infuriating at the same time, as if I'm so unbelievably uninteresting that the conversation has to end.
4. It is ill-bred to put on an air of weariness during a long speech from another person, and quite as rude to look at a watch, read a letter, flirt the leaves of a book, or in any other action show that you are tired of the speaker or his subject.
In today's world, smartphones are the biggest culprit. If I'm talking, and my partner looks at their phone and checks messages, I find it rude and, again, I feel uninteresting.
8. Never, during a general conversation, endeavor to concentrate the attention wholly upon yourself. It is quite as rude to enter into conversation with one of a group, and endeavor to draw him out of the circle of general conversation to talk with you alone.
I have too many "friends" that do this. I know I'm not exactly immune, but if the conversation is 95% them, yet again, I feel unimportant and uninteresting.
37. A lady of sense will feel more complimented if you converse with her upon instructive, high subjects, than if you address to her only the language of compliment. In the latter case she will conclude that you consider her incapable of discussing higher subjects, and you cannot expect her to be pleased at being considered merely a silly, vain person, who must be flattered into good humor.
I think a little bit of interspersed flattery to a girl is okay, but I agree with this.