Because of boring and longwinded reasons, I can't currently prevent this person from coming to stay with me whenever they like. But I don't have to treat them like a guest, because guests are invited. I have plans in place to renounce this obviously terrible arrangement as soon as possible, but in the meantime I am relieving my frustrations by plotting small, petty revenge's that aren't unreasonable.
(They have a lovey home of their own, and don't really want to stay here. They are choosing to be here specifically because they know I don't want them and to make the point that they still can. It's silly and childish and I didn't choose it. They did, and are also deliberately prolonging the situation. There's nothing to do but laugh about it, and this is intended to be in jest. Although I can't promise I won't put one or two into practice if there are good suggestions.....)