Finding a Borders' cafe beverage cup (the clear kind) completely filled with green mold and brown sludge in the exercise DVDs/music section.
Not only did some idiot decide that they didn't want their drink and left it chillin' there (though the tiny amount of a heart I have left is saying "well maybe they just forgot it"), it was sitting on top of a tall center-aisle DVD thing. From the level of molding going on, it had to have been there for at least a week. I'm only 5'7", with bad vision, and I noticed it from pretty far away. So that means that no Borders employee had been to that area with their eyes or nose open for that amount of time.
Good thing they changed to crappy Seattle's Best anyway or I'd be mad that my stomach turned at the sight of a Borders' cup from that day forward.
And I've now realized that I've made a few bad puns, I apologize. But not really.