Im sure you guys know about this one…
its by far my favorite and i obsses not only about cracking mine, but cracking other peoples. My GF gets annoyed mostly but i will always try to crack her secert thumb joint whenever i can.

So, where is the secert thumb joint?

its in the web of the hand, at the base of the thumb, opposite the large meaty part of your palm. If you picture that all your fingers have three joints exposed, and then look at the thumb, its easy to see the thumb only has two joints exposed. the third joint, in the web of the hand, is the one im talking about. its so nice.