Urban Dictionary

1. Man-boy:
(n) A male who, by age, should be a man, but still acts childish, is oblivious of what acting grown-up is about. An insult to point out ridiculous immaturity. A pathetic example of taking responsibility or manhood.

I'm not sure that the second sentence makes any sense, but hey, that's what you get when any yahoo can post their definition. I think it's a good description overall, but I think Grant has graduated to "drama queen." More to follow...