Somewhat of a rhetorical question, where one fellow male asks another if he's admiring the aesthetics of your body definition, or weight lifting ability, when in reality it is actually quite obvious.
Josh finishes a set of dead lifts; with impressive form and weight - when he looks over to his fellow mate, who seems to be struggling with curling 30 pound dung bells. He says " Hey, Steve, U Mirin' Brah? " - Steve replies "No way man", and continues to finish his set.

Josh smirks and flexes in the mirror, and says to himself - " Yeah.. he was definitely Mirin' "