Messy coworker who never cleaned up their mess

I was an office manager for a small family owned business. At the time this happened we only had about ten people working out of our offices, and some of those people were only in the offices for a few hours a week. But we had five people in the office full time. We have a small break room area with a refrigerator and a microwave. Everyone kept drinks in the refrigerator and a few people brought lunches occasionally, but only one person brought their lunch everyday. We will call this person J, now not only would J bring lunch daily she would keep all kinds of food in her office and in the refrigerator. The problem was often times J would leave food in the refrigerator for weeks at a time and it would go bad and start smelling and just taking up room needlessly. Now J was also the primary user of the microwave but she would never cover her food and the microwave was always dirty which was why no one else used it.

So I had to set a new rule that mostly only effected J, the refrigerator had to be cleaned out every Friday and you had to take your stuff home or toss it. Also J was instructed to clean the microwave every day. I was always the last to leave on Friday so I started tossing J's food on Friday after she left. This got her attention quickly and she would take her stuff home from the refrigerator but she still wasn't cleaning the microwave. So once in great while I went to use the microwave and it was disgusting and gross and J was gone for the weekend. So I ended up cleaning the microwave just so I could pop some popcorn. After I popped my popcorn I climbed up and unplugged the microwave and put an "out of service" sign on it. The next week J came in and was shocked when the microwave wasn't working. I told her I tried to make popcorn and it stopped working. She asked when it would be fixed, I told her it was pretty low priority so I didn't know. The microwave was left unplugged for over eight months and the only person who ever asked about it was J. Finally she mentioned it to the owner and he came to talk to me. I explained the situation and he just had a good laugh. J was later let go because of other reasons, after she was let go I plugged the microwave back in, and the microwave was always clean without J using it.