@Summer64 If you're going to host a room in your home, you need to not be afraid to mention things to guests who are clueless about how to be respectful of you and your home. Of course there are some guests who will tend to leave a bad review if they were called out on something, but if you approach it in a polite way, which I'm sure you would, that is not necessarily the case. We can't allow guests to make us uncomfortable in our own homes just because we're afraid of getting some low stars.
"Hey, XXX, I noticed when I walked by your open bedroom door that you have wet towels over the chair. That will ruin my chair, it will leave mildew stains that can't be removed. (Or damage the wood, whatever) I'd really appreciate it if you'd hang wet towels on the towel bar. Thanks a lot."
Some people just don't have common sense, are too young to understand these things, or have only lived in furnished rentals where they haven't actually spent a penny of their own money on any furnishings or appliances, so simply don't get it.
As far as the bathrobe thing, you could mention that as he's sharing a home with a single woman, it would be appropriate and respectful to get a bit more dressed when he's in the common spaces, as it makes you uncomfortable.
Most guests won't be offended to point out things that are a problem for you, as long as you don't keep harping on every little thing they do wrong.
One good way to talk about these kind of things to guests without them getting bent out of shape about it, is to just casually mention it after you've been conversing about something else non-contentious. Say you've been talking about a good retsaurant down the street, then you say, as if it's an afterthought, rather than something pointed, "Oh, by the way, I meant to ask you....."
