There's always that silent (or spoken) rule that you clean up after yourself. You learn that as a child. I understand it's different when you're in your personal space like your room or desk, but when you share something like a kitchen or living room, it's just common courtesy to clean up after yourself. When you get to share even smaller spaces like the fridge or the sink, I feel like that's just a disaster waiting to happen.
One day, I walked in the door and it smelled kinda funky. I subconsciously I made a face like this:
At first I thought it was the toilet again...(we all know what happens in there) and then I thought, "Well maybe it's the devil's cologne..?" (the pumpkin spice air freshener for the bathroom...). It wasn't either of those things! I walked into the kitchen and it was just so ripe. I went over to the sink and there was the source. Half of the sink was full of nasty, dirty water with dishes floating in it, being "soaked" for their own good. I then saw they were Shelly's dishes. I tried to be cool, I counted to ten, did some breathing exercises, but eventually I just had to tell myself that if it wasn't cleaned up by the next day, I would need to confront her.

Of course, it wasn't cleaned up by the next day...in fact, it was worse. Shelly liked to make herself some good steak every Sunday and usually didn't finish it. She just threw the uneaten pieces into the sink, along with potato chunks or whatever she ate with it. Not even trying to put it down the disposal. It smelled horrific. Shelly then came waltzing into the kitchen and I casually asked her if those were her dishes still in the sink. She said they were and I asked when she was going to clean them. She simply replied "They're soaking." In my mind I relayed probably three or four ways I could've choaked her...
I told her it was starting to smell because of her left over food on the other side of the sink. She promptly went to the bathroom and grabbed the devil's cologne. It was like it happened in slow motion. She started spraying it all over the kitchen.
I just had to run out of there. I honestly could not believe the smell could get worse. Then it did. You know that saying, "It can only get better from here." yeah, that didn't apply to this situation apparently. I just had to leave. I let some steam off at a friends place and returned some hours later to a surprisingly fixed kitchen. I'm pretty sure windows and doors were cracked to release the toxins. Nonetheless, life was good again.