Refers to the way men think in regards to their lack of finesse and attention to detail in general; particularly, though, in socially sensitive ones. Much like using an ax instead of a scalpel to dissect, or a shotgun instead of a sniper riffle to shoot a target.
Anyone exemplifying the man-brain lacks the etiquette to handle delicate or intricate social situations as wells as critical thinking that requires consideration for all the problem's aspects.
When a son tells his mother to move her feet so his girlfriend can sit in an effort to "act more like a gentleman" as the mother has been advising him to do. The son is showing a clear case of man-brain.
Usually to describe a person. "He's invincible." A man who is too powerful to become defeated or overcame. He is a tall, hot, muscular man who usually is a hero to many. Although sometimes this invincible person is a faggot, he is a very lovable person. <3 He is originated from Pakistan and his gf calls him "Arse". Lmfao. He thinks he can beat his gf, but he's wrong cuz she has more muscles and is stronger than him. But he's an invincible nigga! So don't mess!