This going to be massively identifiable if the culprit is an MNer, but anyway...
We have a downstairs toilet with a macerator on it. I had a friend round with a potty training toddler who had an accident, so she went to the downstairs toilet to clean her up. Later that evening, I discovered that the toilet was backed up and the macerator wasn't working. There was a suspicious looking wipe floating in the toilet.
Dh and I tried to unblock it but had to call in a plumber, who has just left (with a large chunk of cash). There was what looked like half a packet of baby wipes in there. Not even flushable wipes, proper tough Johnson's type baby wipes. Some of them have been pulled through into the motor and it's fucked. Going to have to get a completely new macerator at exorbitant cost.
I'm really cross with myself for not mentioning that you can't put anything but toilet paper into a macerator, but really, would you put a whole load of actual baby wipes down someone else's toilet? Or even your own?! My friend is lovely and has done lots for us and I can't bring myself to mention this to her but I am just so frustrated.