your friend asks you to house-sit for a week while she's on holiday....by the time she's come back you have re-arranged all her furniture, cleaned up the spare room, changed the location of the bird baths outside, cleaned out the fridge/freezer (and had to chuck out most of the contents because they were past their expiry date), got stubborn stains out of the carpet that had been there ten years (because stains just annoy you), used up her download limit (because you didn't realise that she had a limit...) and started letting her inside only cat play out in the backyard during the day because he seemed to enjoy it.
I've never understood why people say "make yourself at home" when they quite obviously don't mean it literally.....