One of the only well developed muscles on gamers, especially those who have yet to grow pubic hair.
During an argument the kid or effeminate dude in his parents basement will mention how awesome he is and something about your mother
"I can't believe you lost the game for us! I was trying so hard (tears forming)... hard like my 13 year old dick with your mom!"
"Really man? Did you just rip off your bieber T-shirt and flex your Microsoft Muscle?"