Or, the one that I am guilty of. Forgetting to purchase one item on the list as the Cashier is still ringing up your order, and having to leave the line and run to the "other end" of the store to retrieve it, while the other shoppers in line just "glare" at you as you make your way back to the front of the check out line with the "forgotten" item in hand and a "sheepish" grin on your face. Not a pretty picture.