The act of somebody placing a hand on the opposing shoulder, and then leaving it there, as if fondling their own shoulder blade. People usually shoulder-grope themselves while discussing their accomplishments or positive traits (often with a sentence beginning "I'm pretty much the best..."), and it is therefore regarded as a narcissistic celebration of one's own awesomeness. On occasion, both hands are employed, giving the shoulder-groper the appearance of somebody hugging themselves because they have no friends.
I don't mean to brag, but *shoulder grope* I'm pretty much the best clarinet player in the whole entire school.
by RAGNAAAAAAR! June 18, 2010