DEAR MISS MANNERS: When living with roommates, do I have to inform them of when I have a guest spending the night? If I do, how much time in advance is appropriate?
GENTLE READER: While using a popular online language program, Miss Manners dutifully learned a sentence that she could not imagine anyone would have occasion to use, in any language. It was, “Who is that man in the bathtub?”
But indeed, you have posited a situation in which it might be useful.
Nevertheless, it might be better if that situation did not arise. Roommates need to agree on house rules, including a policy on guests -- and apparently, in your case, last-minute guests. It can be whatever you all agree on, but Miss Manners would think that “no surprises” would be a good guiding principle.