Tell us the theme!!
My DH would NEVER do it
Hope there are no lurkers here that I don't know about...but here goes. My DH has twin sisters that are having a milestone birthday

this year. He has asked me to plan a surprise party for them as he feels they are deserving and that their husbands would not do anything particularly special for them.
I have planned the party with a Fabulous Fifties theme and the invitation states "Dress to impress in your fifties best". We have invited coworkers, old high school friends, neighbors, friends from church etc... and our (large) immediate family.
The party is in a banquet hall with DJ, dinner, tons of balloons, rented pink, black and turquoise linens, and even decorations from a company that supplies party backdrops/decorations for proms.
The party is Saturday night. My Dh's other sister informed me yesterday that her three children (ages 17-8) don't feel like dressing up and would not be wearing
a costume. I'm really put out by this. I have taken this opportunity to tell my DD that you either accept the invitation, as is, or decline if you don't feel like participating.
I am not expecting anyone to go to a costume rental place or even buy a Halloween type costume. A few adults have asked me when they called in their RSVP "how serious is this 50's dress?" I have replied, "capris and tennis shoes would be fine or white t-shirt rolled with a pack of smokes and a leather jacket, hair slicked back, for the guys. Nothing major, just come and be ready to have a good time."
So that's the deal, hope I haven't blown the surprise... I really wanted to know if I'm that out of touch with what is acceptable party etiquette these days.