U.F.O. day Share definition Flag The one day during the menstrual cycle when you are in such pain that when you stand up, it actually feels like the uterus is falling out. No, I can't go to aerobics tonight......I'm having a total U.F.O. day! U.F.O. day by fsara April 9, 2004 0 0 Get merch Get the U.F.O. day mug. Buy Now — $32.95 See more merch
