I once found a USB key in the office car park when I arrived at work on my bike.

It turned out to have a series of pictures of a man and various (many!) women doing the naughty. The man's face was never visible, but there were a bunch of e-tickets for flights as well. These were in the name of a married senior colleague.

I anonymously stuck it in the internal mail for him. Never quite felt the same when passing in the corridor!