The first time I realized the danger of Easter eggs was one that was triggered by Alt+Ctrl+Shift+PERIOD or some such. Tested it out and sure enough it would paste an email exchange about needing to add an easter egg into a comment field.

Then I was demoing the software to leadership in a surprise visit, and it triggered. Turns out, I'd ORed the keys together! I tried to Ctrl-A+DEL but... the email was longer than the comment field and triggered a state in which any keypress was rejected with an alert, even one that would shorten the comment (bug #2). And I couldn't leave the form, as the early prototype was designed to save-on-exit. So I had to kill the app... lesson learned.

My last easter egg was simply the name of "Lightish Red" for one of the AI colors in Halo Infinite. Much safer (once it got through localization, hah).