The Ladies' Book of Etiquette, and Manual of Politeness

Upon your way home from the theatre, concert, or opera, speak warmly of the pleasure of the evening, and, at parting, thank him for that pleasure. Show by your manner that you have heartily enjoyed the entertainment you owe to his civility. If you are weary, do not allow him to see it. If disappointed, conceal that also. You will be able to find some good points in the performance; speak of these and ignore the bad ones. If at the theatre, opera, or in a concert-room, you see an acquaintance, you are not expected to recognize her, unless near enough to speak. A lady must not bow to any one, even her own sister, across a theatre or concert-room.