[gtc]

I use a pocket knife all the time. My method:
Hold beer by the neck with left hand, just below the cap.
Hold an open knife facing away from you with your right hand. Rest the knife blade on your knuckle and put the square back edge of the knife under the cap.
Roll right hand forward, using your knuckle as the fulcrum to pop the cap with the back edge of the knife.
Easier than a bottle opener once you get the hang of it.