At a company I used to work for, if someone left their computer unlocked, we'd send the donut emoji into the #everyone channel on slack from their computer, and they'd have to buy donuts for the office
We had a similar thing at one gamedev place that I worked at where and email would go out to the team if you left your computer unlocked(I forget the exact phrase but it was fairly silly).
We had shared offices and one of the programmers had the office right next to the kitchen. One day we all heard the senior programmer shout "WHAT THE FUCK!" and all ran over to see what had happened.
It turns out one of our engineers had walked into the kitchen and left his computer unlocked. The senior developer seeing this had opened up outlook, started a new message and began typing in the subject. What he didn't know is the developer had hand-rolled a keylogger with a match pattern for the message that everyone would send and dispatched Windows+L via key injection to the main window loop.
The trap was sprung and the machine locked right in front of him as he typed the last letter unable to send the email.
There was all sorts of other shenanigans at that place(like a fake "April 2nd" firing, they got the person who did that back with an annoy-a-tron over a 6 month period) but that was one of the more memorable ones.
Edit: Also singing over the top praises of employees using the victim's account. "MonkeyButton is truly the best coworker I have ever had "
All this fun has gone away now with Covid and remote working.