Vault 4200:
All occupants other than the overseer are constantly kept high, given weed with all meals, and convinced that it is essential to their survival and that they will die without it. All occupants are told and convinced that not being high for more than a couple hours will be fatal, and weed is used alongside all medical practices as well.
or
Vault 124:
All original occupants are androgynous in appearance or are surgically altered to be so. The concept of gender is completely unknown in this vault, with nudity beyond underwear being taboo and birth by artificial insemination or by cloning. To keep the concept of gender completely hidden, hormones are added to all food, and everyone is either given breast reduction or breast enhancement surgery.