Hi cracking_up,
I too play a contact sport (rugby) which has enabled me to crack many more joints than would otherwise be possible. One particular tackle, in which I broke my coxics, has left me able to crack that area just by tensing it and bending backwards slightly. My knees and elbows also crack daily from previous broken bones, and rather than be irritating, this actually helps me release some of the pain I get there and feels fantastic.