your friends awkward, often creepy and more times than not, inapropiate boyfriend. It's not that these gentlemen are intolerable individually but when with a large number of their girlfriends girlfriends, their "manshadow" qualities are more pronounced. Often the manshadow will only talk to/address significent other, giving him a more hollow persona, hence shadow. Usually uninvited.
(Linguistic credit goes to Alex)
"Oh my god, she brought her manshadow with her." "Is it a girls night? Yeah, no manshadows aloud"