People at my company don't even lock their computer when they walk away from their desk. Which yeah it's in a controlled environment but still.

My work has a “donuts” slack channel for this. You find an unlocked computer you post “donuts on me!” Social pressure says they buy the office donuts.

Still get a few a week, but at least it’s public and amusing.

We used to flip display upside down in display options, which also reverses the mouse. We'd then lock the PC and disconnect the keyboard. After they figured out the keyboard had been pulled they often couldn't work out why their screen was upside down...