chico has deep wisdom, and explains it better than I can. It's a hard thing to explain, for it's not a binary thing; it's more abstract that that, and each has it's own shortcomings as it were. It doesn't really have anything to do with level of Machismo or intelligence, but most in how a male approaches problems and how they interact with others that plays the biggest part in the Guy-Man-Boy thing. I'll try to use my earlyer example; owning an old car, to explain:

A man drives an muscle car because it's cool; a boy drives a muscle car because he thinks it's a cool thing to do; a guy drives an muscle car trying to look cool. A man takes responcibility for this car and fixes the car himself if he can, or pays another man to fix it if he can't. A Boy fixes the car, or pays someone else to do it, but doesn't know why or really care how it works. A Guy fixes the car, or pays someone else to fix the car, and then brags about it to other people. A Man loves the car because it's cool and something he put real work into, the Boy loves the Car because it makes him look cool, and the Guy talks about the car to random strangers to show how cool he is.