I've seen it many times, and also these classics:

• Elderly couples entering the store with a shopping cart, then stopping immediately behind the entrance - "Oh, won't you look at all this stuff in here? Now what do we need again?", completely oblivious to the queue forming behind them.
• Old people standing in the middle of aisle intersections with their shopping carts like statues, just... pondering.
• Old people very slowly paying with coins at the checkout, like one cent at a time.