Some dogs get excited at the weirdest things. If you've noticed your dog freaking out when you take his collar off, you need to look beyond the act of removing the collar to discover the cause of this excitement. For example, he may associate collar removal with freedom, or indeed the end of playtime. Or it may simply be that he hates being touched on his neck. Observe his accompanying behaviors to find the cause.
If the collar is too tight, or if your dog has a cut, bite, muscle strain or other injury to his neck, the area will be tender to the touch. The act of removing his collar may cause the dog physical discomfort, causing him to react excitedly. Examine his neck for signs of injury to rule this out. Then try leaving the collar off for a few days, before seeing if he'll let you touch his neck without freaking out. If he still freaks out, it's the contact with the neck, rather than the collar, that is causing the problem. The next step should be a visit to the vet.
Intolerance to Physical Contact
Some dogs just don't like being touched. This can be due to a personality trait or simply because they weren't properly socialized as puppies. Compare his reaction to having his collar removed to other known reactions. For example, consider whether his reaction is similar to a fear reaction, such as hearing the doorbell or vacuum cleaner. If so, it's possible that he's anxious about physical contact.
Dogs learn by association and yours may have identified the collar as a trigger. This is called operant conditioning. For example, if you only remove his collar when you're about to let him run free in the field, he'll naturally learn to associate collar removal with that wonderful sense of freedom. It's no wonder he freaks out.
Behavioral triggers can cause distress too. If your dog only wears a collar when he's out of the house, he'll soon come to understand that having his collar taken off signifies the impending end of his walk, or playtime.
Curing the Problem
If the freak outs are linked to an injury, let your vet fix the problem. Once the pain is gone, gradually reintroduce your dog to the touching sensation. For dogs who hate being touched, a carefully managed process of desensitization may help. If necessary, enlist the aid of an animal behaviorist. The process will gradually help the dog make neutral and positive associations with being touched. If the freak outs are caused by behavioral triggers, simply altering what happens after the collar is removed will help your dog learn not to get excited. For example, if your dog gets distressed, give him a food treat once the collar is removed. He'll soon learn to love having his collar removed.