I crack my knuckles all the time....

I can crack virtually every joint in my body. All my vertebrae, my coccyx (tailbone!), shoulders, elbows, wrists, thumbs, all three joints in my fingers, my hips, my knees, my ankles, my feet (at the ball of my foot, the part that bends when you step), and all of my toe knuckles.
When I get up in the morning it sounds like bubble wrap! :D
Also, it does nothing to you medically. All the arthritis stuff was disproved. It's fun, feels good, and is handy when you want to gross someone out or impress a kid (say when babysitting).
Crack away!