The common claim that "cracking your knuckles gives you arthritis" appears unsupported. A recent study examined the hand radiographs of 215 people (aged 50 to 89) and compared the joints of those who regularly cracked their knuckles to those who did not.The study concluded that knuckle-cracking did not cause hand osteoarthritis, no matter how many years or how often a person cracked their knuckles.
Don't listen to these people ^^^ if you crack you knuckles enough it could effect your fingers strength and quickness in the future. It really messed up my grandfather and he had to take physical therapy a few years back. I don't know much about cracking your neck but I'm sure that could be unhealthy as well, better safe then sorry :)