It is customary for officers, and should be for men as well, to remove their caps before entering a mess other than their own; this custom applies equally to officers’ messes and enclosed messes, and should be observed when passing through seamen's mess decks except on duty. The customary rule applies to cabins and offices as well. This is the same as the practice ashore -- you do not wear a hat in someone else’s home, and though you may wear it in your own home you would not normally do so.
