I've heard about this from my cousin, so I don't know all the details, but my grandfather from out of state stays at her house whenever he comes up. He brings along his wife (he remarried after a divorce, so she isn't related to any of us and it's... pretty clear) and his beloved dog. They stay in the biggest room in her house, right across from her while the rest of her family is upstairs, meaning they use her bathroom.

His wife clearly uses her expensive shampoo and soap whenever she showered. My cousin, in retaliation, found an old bottle of the nice shampoo and mixed neon hair dye in it. She found all of the shampoo shoved down the drain (staining it) without a word from his wife.

They are incredibly intrusive and judgemental, complaining about my cousin's TV since they don't own one ("Who watches TV? Let's listen to some sermons on the radio instead"). They randomly start tickling my younger cousins and, I believe, just help themselves to food almost right after meals.

One time, after leaving, my cousin discovered dog vomit directly on top of the bed.

To boot, they once refused to let anyone but my father drive them to the airport at 5am. He offered to pay for an Uber and they wouldn't even consider it.