Thanks so much Bill for posting this question since I always yell at someone who does that. However there is no evidence that cracking your joints are bad either. Whenever i see someone and see that "cracking" sound it is normally associated in most cases to some muscular or soft tissue disfunction: either they are tights or some soft tissue are not aligning properly. The crack sound sometimes can be pure gas created when ligaments, tendons and
A joint is comprised of bone structure surrounded by soft tissue including smooth cartilage, which is covered by a capsule with synovial membranes that produces fluid. However is the fluid that causes sometimes the crack. This fluid contains oxygen, nitrogen and carbon gasses. When joints crack, it could be the result of the joint capsule being hyperextended, which causes the formation and release of gas bubbles that make that "cracky" sound.
However every time you crack the joints your naturally hyperextending the soft tissue with possibly damaging it so if you can stay away from cracking your joints voluntarily.
Hope this helps!
Ofcourse it helped! thanks a lot ;)