Sounds horrific. Some dorris just wanting to convince herself she’s inportant by forcing a stupid dress code on people. A crisp tenner (of someone else’s money obv) says her bosses turn up in jeans and whatever the fuck they want to wear.
Only one thing for it. Go full retard. Turn up in a Mr. Blobby costume, claim you misread the instructions, completely wreck the joint falling all over the place. Leave. No more shit work do’s ever (either by virtue of company policy changes or just plain old being fired for gross misconduct. Either way sounds like a win - take up the ‘dealer ‘n’ dj’ route suggested above instead)