I've started watching the tv show Flip or Flop on HGTV, following a married couple who flip houses and I saw one that was absolutely horrifying.
They bought a foreclosure at an auction, without touring the inside, based on the neighborhood and square footage. Once they got into the house, they found that someone had vandalized the entire house: breaking every window, slashing the blinds, and smearing unnamed substances on walls and floors. The worst part, though, was that every sink, toilet, and tub had concrete dumped into the water, where it then hardened. They had to replace every single one of them, and a large portion of the plumbing.
I know foreclosures get vandalized, but I think the worst part for me was the creativity with the cement. That was one I'd never heard of and I was amazed (in a bad way) that somebody would think to do that.