When a boy (in the mental sense) goes through a dramatic transformation to become a man's man.
This may or may not involve things like working out consistently and losing weight, learning to finally respect what women have to say, spending thousands of dollars on a new wardrobe, and sporting a pair of hipster glasses.
An overpowering, possibly even devistating amount of manly fantasticness such as the ability to pull the hottest chick, drink the most beer, or nail the best trick.