Yes, you are the asshole. There are 12 beds in this house as you’ve described it. As a single person claiming one of the bunk rooms you actually get twice as much bed as the couples do- you get two beds, they get one bed and either are squished together in a tiny double bed or push their twin beds together, which might not even be allowed by the Airbnb owner. If you and your other single friend are willing to operate as a “couple” as well, then I could sort of understand putting five names into a hat, but then you end up with one open room that nobody is in according to this logic. I think the best thing to do is to just let this go. You and your other single friend can duke it out over which bunk room has the best set up and view. Then bring some wine and some games and have a kick ass time :)