Gentlemen should help a lady with her coat, cloak, shawl, or other outer garment that she desires to remove in order to be more comfortable in the room. Offer to fetch refreshments for a lady if refreshments are available. It is impolite to spit in public, and most particularly around ladies. Gentlemen are also not to use tobacco in any form when ladies are present, but to reserve the indulgence of their vice for the company of men. As a general rule, it is also considered a serious breach of etiquette to dip from another person's snuff box - unless the dip from another person's box is first offered to you.
Loud conversation is, in and of itself, a great social faux pas.
Writing on a wall, sitting on the floor, or throwing things onto the floor are glaring vulgarities as well. Even stamping the feet at a dance is a faux pas. No gentleman would presume to look into such a place. Entering it would be an outrage that would not brook forgiveness. Cleanliness is always appreciated.