Stuffing copious amounts of food waste down the garburator & completely blocking the kitchen drain, not telling us about it for over 24 hours, not answering when I wanted to send a plumber, then leaving all the dishware & utensils in the place dirty & filling every pan, cookie sheet, roaster pan that I own with them. Leaving cooking mess all over the stove top. Then leaving me a note to say I have a really nice place & they'd like to come back again soon.
Taking my phone charger, admitting to it, then refusing to pay for replacement.
Using almost every bath towel in the place after only a 2 day stay (22, over 40 towels in all with hand towels & facecloths, 7 people), leaving them laying around everywhere, throwing the bedspreads & duvets on the floor. Leaving the thermostat cranked up to 25 C.
We've only had 5 separate groups of guests so far - 3 were awesome, 1 was awful, 1 was semi-awful.