I posted this elsewhere but I will post it here too, try to give him a sauna and then use Q-tips to gently remove the shed. It looks like it is constricting bloodflow so you need to remove it asap. This happens and sometimes some reptiles need a little help shedding. If your crestie was in sub-optimal care before you got him (some stores do not take care of their cresties right) he may be recovering from bad treatment and could have some bad sheds for awhile, or your crestie just may be predisposed to having trouble with tail sheds. I would definitely try the sauna and keep an eye on him while he is shedding for the next few sheds so he doesn't end up losing his tail.
