Yes, you can rip a bike tire from a rim with nothing but your bare, gnarled hands, but a lever makes things a lot easier. I use two (from a set of three) and keep them in my toolbag at all times. If even that is too much for you (and you haven't yet mastered the art of bareback rubber removal) then may I present the Cobra Tire Tool, a single, solitary tire lever.
The half-ounce plastic lever is guaranteed for life, and looks very simple to use. You hook it between tire bead and rim, just as with any other lever, but then you hook the looped section around the fork (or chain-stay for the rear wheel) and it locks in place. Spin the wheel and the tire peels open like a tauntaun's belly.
It doesn't seem to make it any easier to put the tire back on, which is the part that taxes even my calloused thumbs, but the hooked lever should work just as well as any other lever in this case (and you're supposed to use just your hands to replace the tire anyway).
The Cobra Tire Tool is available now, for a reasonable $6.
Cobra Tire Tool product page [Cobra Tire Tool via Urban Velo]
