If you lack for a ring, Wired explains the time-honored tradition of popping the top with a Bic-type lighter.
The hands pictured above and at the How-To Wiki post aren't actually in the safest, most efficient position for cap removal, even if it works. The lager-friendly writer at Wired explains exactly how to place your digits, and writes elegantly on how to work them:
Squeeze the hand that is grasping the bottle to create pressure around the cap, while, in one swift motion, you grab the top of the lighter with your other hand and push the lighter down like a lever, with your forefinger around the cap acting as a fulcrum.
Use your thumb instead of your forefinger, as you might naturally do, and you could direct the cap toward your face, which is a bad idea under any circumstances.
If there's an emergency bottle opening technique we haven't featured here, let us know about it—we are, apparently, building quite the collection. Open a Beer Bottle With a Lighter [Wired How-To Wiki]