Is it wrong that I   grab my dog's back legs and dangle him upside down.
Why are you abusing your dog?
I want to mess around with him, the dog that is.
That is an immoral thing to do to an animal, you are abusing and harming it. You are losing its trust and you aren't treating it kindly. Your actions are against the law.
You are acting crazy. He's a big dog and he doesn't seem to mind.
I am sure that your dog does not like that. You need to take better care of it. If you don't trust my opinion, ask an expert for their thoughts on it.