Ugh, flashbacks to my aunt's 50th birthday party a few years back where the dress code was white and gold. Unfortunately, no one actually told the family. (It wasn't made clear on the invitations; they told their local friends the dress code at the time, my uncle was meant to have shared it with his side of the family - hers weren't present as they're all in her home country - but he forgot).
My one cousin did come out and ask (although he later decided he couldn't be arsed to find something in those colours, and his wife had originally had a clash and couldn't go. By the time circumstances changed and she was free after all, it was only a few days to go and she didn't have time to look for anything white or gold) but none of the rest of us found out until about two days before the party when that cousin was messaging his sister, she told him what she was wearing and he said "But the dress code's white and gold!" She then promptly messaged the rest of the family, found out none of the rest of us knew (and on two days notice, had no time to do anything about it), then messaged our aunt to explain what had happened. At the time, the aunt said it didn't matter.
We all get there, first person we see is our uncle who's wearing a dark suit, cousin's wife says "He's not even keeping to the dress code himself! Do you think that was a joke?" Cue everyone else walking in wearing white and gold, and aunt made it clear that actually she did mind that we hadn't kept to the dress code, despite it not being our fault. When she put her photos of the party on Facebook later, she made a big show of only posting pictures of people in white and gold, cutting the family out.
Anyway, point is, it wasn't anything I'd heard of as a thing before this party (this was in 2017) and the experience left me pretty anti-dress code. Liking the suggestions people have had of dressing as someone like Shrek, and if my family have this crap at a party again, they can stuff their dress code.