I didn't go in meaning to do this, but I allowed it to happen... there's a coffee shop in my city that I always stop by on my way to work. About seven years ago they were selling some travel mugs, so I picked one out, brought it to the counter, had it filled with coffee, bought some water & a shot of espresso and payed with my debit card... I got the receipt back, wrote the tip, then noticed that the ticket was way cheaper than it should have been. I did it, felt like shit, and went back and bought two more.
Beyond that I got nothin', unless you count downloading movies.