The male g-spot is reached by stimulating a man's perineum and ass!!!!
The male g-spot (it's actually called the A-spot) is a walnut shaped/feeling lump that's located right beside the prostate (it's NOT exactly the prostate unlike what many say). You massage it, and you'll feel it, and for most men, it creates a feeling of extreme pleasure. A lot of men will say it makes them feel like they have to pee. It's a very sensitive feeling; basically, it's something that keeps you on your toes, it can be pretty overwhelming. It's why men like to have their asses played with, because the ass has sensitive nerve endings that make stimulating them pleasurable, and because of the A-spot.
When men say their ass is exit only, I can only shake my head at what they're missing out on!