The act of first, filling up your grocery cart, but then upon deciding that you could get the items cheaper elsewhere you put all the items back where they belong, thus emptying your cart.
Scene: Girls shopping in grocery store together with 10 or less items in their cart.
Girl one: "Girlfriend, I don't think I have enough money for these things in our cart."
Girl two: "You're right, we could get these same things cheaper at one of those 'one-stop-shopping' stores."
Girl one: "Let's do some unshopping here and head off to Walmart."