People who fix computers/laptops, what's the worst thing you found on someone's computer?

All the internals of one laptop I opened were really covered in oil, the fans were totally stuck and unable to spin (maybe the main reason why they sent it to us) and the whole thing really stank. I called the customer to ask how was that possible and to inform that those defects weren’t covered by our warranty and they told me it was used in a restaurant’s kitchen, and they didn’t understand why they couldn’t use it there.