Hi Erica,
Sounds like it could be a case of either one or actually both— you being a little bit sensitive and this crop of guests being particularly terrible. You won’t know how terrible they’ve checked out or you knock on the door and get a look inside. It kind of sounds like they might be the pretty inexcusably terrible variety. Hopefully they aren’t staying very long!
You say you live in that apartment above, so there are a few things:
1) since it’s convenient, always try to meet the guests at check in or within 12 hours of their check in.
2) change your listing to emphasize that you live upstairs and this listing is absolutely not for partying or any illegal activities, and no smoking inside or out.
3) please don’t be shy about giving these guests a very low rating they deserve so other hosts don’t book them
4) now that you’re learning more about hosting, you’ll know to talk about being respectful neighbors, noise level, etc. in all the house rules. Be very specific and harsh in your listing to scare off anyone who is even contemplating those things.
5) the vomit stained linens may have to be a hard lesson, but don’t lose out hope that a good laundering may still be able to save those items, and that they just may agree to your extra charges for them. Maybe!
6) as ive done this more and more, the very cleanest and most respectful groups of people are families with mothers traveling with them. The least clean are the groups of youngish friends— in my experience males being worst. I know I’m stereotyping and this is definitely not always the case, but the theory is pretty strong.
When do do they leave? Are you stuck with them for very long? If they are staying another night, i’d knock on the door with a bunch of water bottles or something and let them aware of your presence in the building. If you can strike up a conversation on how their visits going maybe you can take a peek inside.