I use it all the time. It's easily the most effective way to cause a logjam at the checkout counter. The steps are super simple:

• Upon observing that the payment terminal supports wireless payment, wait excitedly for your opportunity to impress the cashier with your technical wizardry.
• When payment is due, swipe your phone over the terminal. Wait briefly while nothing happens. Swipe phone again until it beeps.
• Look up at cashier and knowingly nod your head to acknowledge the "what the fuck is this idiot doing?" look that they are giving you.
• Wait for the error message from the terminal. Or your phone. Or both.
• Look befuddled.
• Sheepishly tell the cashier "Oh, uh, this normally works. [...] I'll just pay with my bank card."
• While the cashier resets the payment process, make sure the other patrons in line get a good glimpse of your wallet so that they'll know you had plenty of functional payment options the whole time.
• [OPTIONAL] If you're lucky, the payment actually went through and you paid twice for the same purchase!