I just realised that egg is a NZ term. It is a very common insult not an overly harshone. Your pretty much saying the other person is stupid. When I was little I would say your an egghead. Now everyone just says your an egg.
Christ, what is wrong with you people ? An egg is an egg. A conjugating cell which unites with another of like or unlike character to form a new individual.
Most talked about is the chicken's egg, usually white or brown in colour and shaped like an oval with a fat end. Alot of people eat them, but vegans don't eat them.
And people who don't like them don't eat them either.
A substitute for when you have nothing else to say; funny with or without context. Although this is incredibly funny with two capital G's, the humor will not be the same without them.