I'm inclined to think neocon is a short version of "kneejerk conservative," unfortunately used to avoid considering the value of some ideas that might just possibly come from a conservative source. Those guilty of kneejerking also come in liberal varieties as well, and mostly they like to use the term neocon liberally (often). ;^)
As someone who thinks for himself, sometimes taking liberal, and sometimes conservative positions; I find kneejerkers on the far reaches of either side annoying. And too often loud.
As for my brother calling me a neocon, I think he's got a fine sense of humor, and I can laugh at a joke where ever it comes from. ;^)