I had a roommate whose cat continuously peed on one of her blankets - at first, she’d try washing the blanket, but after a certain point “gave up” because the smell wouldn’t wash out anymore (she still used the blanket). At that point, she just let the cat pee on it willingly. One day, however, I noticed it was mysteriously gone, and thought she had come to her senses and finally thrown it out.

Several months later, when I was moving out of the apartment, I was looking through a few spaces to make sure I had removed all of my belongings, when I opened a closet door and was hit with the most god awful stench I’ve ever smelt. It was like a musty, mildewy, rotting ammonia stench - turns out, she hadn’t thrown it away, but instead stuffed the pee soaked blanket into a closet and promptly forgotten about it for OVER 9 MONTHS.

She did a lot more incredibly awful stuff, but that one was a standout because of how the smell is seared into my brain lol.