95% humor

The reason was that, if you get pantsed, and you weren't in on the joke / it wasn't planned, that's a massive breakdown in respect and discipline, and you have to make an example of that kid (generally by wrestling them, and in serious cases, taking away candy privileges). But getting pranked is still a bad look, and makes it seem cool to rebel against your authority.

However, if you get pantsed, and you are in on the joke, everyone has a good laugh, including you, and no one was actually rebelling. It both makes you look like a cool authority figure and makes the person doing it look like they're the sort of person in cahoots with counselors. Then, if there's a behavioral issue, you can have that quiet conversation later, away from an audience.

And since those underwear are so culturally specific as punchlines in a pantsing gag that the only plausible reason to be wearing them is if you're in on a slapstick act, you can retroactively Shanghai any would-be prankster into looking like they did it with your consent and planning, which not only keeps you from indignity, it makes sure that they're rewarded by laughter and attention for looking like they're cooperating with the staff, encouraging that in the future and bringing them in from the outside of the social-reward structure you're trying to set up, where it's cool too be wacky but responsible.

That preparation effort paid off maybe four times across three years, but it was completely worth it.

TiL (click to go to the thread, which probably has more interesting tidbits I missed).

Bonus:

In addition to the print terminology stuff: the visual shorthand icons and ad graphics for something about writing are still often pen-nibs, fountain pens and typewriters…

…while graphics of a monitor, keyboard and mouse remain visual shorthand for computing…

…even though most writers now use monitor /  keyboard / mouse or even laptop / touchpad.

In addition, headers for “this blog / website is about writing” are often in one of the many imitation typewriter fonts complete with smudges, or just Courier.

The start and end call icons on most / all smartphones is still the handset of a classic desk telephone, and sometimes the open-app icon is a complete phone.

The term “hang up” for “end the call” refers to something even older - one of these…

And of course the Save icon is indeed a 3½ inch floppy disc.

Why it wasn’t a 5¼ floppy is a mystery. The icon version is just as distinctive.

Also, why various OP updates never changed “Save” to the graphic of a CD / DVD or flash drive is another mystery, and nowadays a Save icon should probably be a cartoon cloud.

In their reply to the audience they then say they are picking her up from middle school, again implying that their girlfriend is underage, but quickly state she’s grading papers letting us know she’s a teacher, definitely an adult, and there no reason to be upset.

The rollercoaster gif portrays how switching from upset and worried to relieved in such a short period of time feels emotionally.