YANBU. That's a pisstake.
I personally love fancy dress and when myself and my Ex-H moved to our village, we popped into the village pub the first week and found out they were doing a 60s / 70s fancy dress for NYE.
We thought NYE was the perfect time to get to know the locals, especially with the silliness of fancy dress to ignite conversation. We made a mental note, but didn't return to the pub over the next few weeks as we were unpacking, decorating, settling in and preparing for Christmas.
Come NYE, Ex-H is dressed up like a Starsky and Hutch character, complete with wig. I'm dressed as a punk, fake piercings, pink and blue hair, with mad make-up.
We rock up to the pub, we can hear it's heaving inside. We walk in and the whole pub goes silent. We were the only two dressed up in fancy dress.
After the landlady stopped laughing, she explained that a regular had passed away just before Christmas, so nobody was in the mood for the fancy dress element, as we'd not been in there since the week we moved in, we didn't know.
We contemplated going home to get changed, but our appearance caused quite a stir, a lot of laughter and broke the ice with the locals in one swoop. 😂😂
I might share this story as an OP to see what other fancy dress fails people have to share. Still laugh now about our introduction to the village.
But going back to you OP, YADNBU!!