The most recent one: when I was in the Army stationed in Germay, we had to close down our barracks to return them to the German government. Soldiers living in these barracks were instructed to clean the food out of their refrigerators, defrost them, and leave the doors open.
Guess a few of them didn't get that memo. We had to go room to room, and clean every single refrigerator. The mold and the stench was absolutely horrendous. And though we were using bleach to clean these refrigerators, the smell of bleach combined with the mold only served to elicite more dry heaving. You'd be amazed how bad a refrigerator full of mold can smell.
The very first one: when I was 14, my stepgrandfather got sick with TB. We'd never been invited to his house, and always wondered why...we found out why one day. After receiving a call from the hospital because they needed paperwork filled out, we went to his house. It was rat-, roach-, and every-other-critter-you-can-think-of-infested. We spent six weekends cleaning out this man's house. We found dead animals, feces galore from the "exotic pets" he sold, nests of mice...the neighbors next door had tried to chop a tree down during his time in the hospital, and the tree fell on the part of the house that was the kitchen.
That was indeed a dirty job. I couldn't believe a human would willingly live in such filth. Six weeks later, when he got out of the hospital, he had two clean rooms in which to live. We ended up blocking off the majority of house, and he had a bathroom, a bedroom, and the front living room in which to spend the rest of his days. Meals-on-wheels delivered to him, so he didn't need the rest of the house. It was the best we could do under the circumstance.