An acronym standing for Group Poop. Much like women and their periods, when men begin living together, their poop cycles coordinate. A group poop is when these strapping young whipper-snappers, members of a team, or other cohesive unit, as it were, congregate to poop together in the same facilities. While defecating, they listen to the collective bowel calisthenics and engage in witty banter or bathroom games (i.e. kicking open the stall door/paper towel bombings). Also see P.I.A.G..
"Hey guys, I'm feeling a little vulnerable, can we go take a G.P.? For old time's sake..."