I witnessed something like this once. I worked for a pawn shop, wiping and reinstalling Windows on computers they were selling, but occasionally working on one of the counters if they were short staffed.

One day a regular customer brought his PS2 in to trade, so it had to be tested first. The manager took it as a training moment for me and and a few others, and connected it to the main TVs around the store so that we could all see how he checked the system.

The customer had left a rather hardcore DVD in the drive and completely forgotten about it, until it started playing on the big screen, and everyone in the store learned about his preferences.