My colleague set an out-of-office reply that said "back Monday." Simple, clear, standard. Except that Monday came and went, and she wasn't back. So the leave got extended. Silently. And then extended again. And again. Three separate times, without the message ever being updated.
So for days, anyone who emailed her got a cheerful, confident "back Monday" that had become increasingly, aggressively untrue. Which Monday? Nobody knew. The message committed to a Monday and simply let all the following Mondays pass without comment.
The team eventually discovered she was back not through any update, but by seeing her suddenly appear on a call. Twelve days after the original "Monday" had come and gone. Just materialized, live, no announcement.
And the best part: the out-of-office message itself, as far as I know, was never corrected. It ran its full inaccurate course. To this day it technically told a small lie to everyone who reached her, and she returned to work without ever addressing it. Deeply respect the commitment to not touching that message again.