Oh. I have one for this. I support people from several timezones, so to help myself, I set up a couple of additional clocks in Windows, so I could keep track of what time it is for the user, since most people are bad at thinking outside of their local timezone.
Well, I’m in a timezone that uses DST, and when it started for my timezone this year, all of my clocks changed. Every last one of them are now wrong, since the actual timezones they are for don’t do DST.