A giveaway sale. Usually a sale when a store or business wants to give away everything.
100% off sales/discounts are sometimes pranks. 100% off sales/ discounts could be used by terrorists to sell hidden bombs, or to sell DVDs, which are actually screamers.
Person 1: Oh, look! There's a 100% off closing sale at Winners!
Person 2: That's stupid.
Person 1: Everything's free! Let's go, before everything's gone!