When a man and another man harbor secret sexual desires for each other (either known or unknown) and use 'many' gestures to express their passion without others knowing. Gestures can include: Back thumping, head locks, and arm punches being held a little too long, and turn into arm around shoulders. Being completely manly of course.
1 goes up to 2 and forcefully pats back as a way of greeting, and lingering a little too long. Fist bumping and holding it there. Coming up behind someone sitting and putting hands on shoulders.
Oblivious people see it as macho men's way of greeting each other, more aware people see it as Macho Gay Touching (MGT)
Can also include things such as sharing meals, and buying matching shirts, even though they are not included in the "touching" aspect.