much like a dirty sanchez, it is when fecal matter is applied to the face in such a way it covers the entire lower jaw and upper lip. it is also typically applied by pirates (homosexual or not) to other sleeping pirates/crewmates/scurvy dogs as a joke. it is punishable by having to walk the plank, getting the shit beaaten out of you, or recieving a brownbeard in an act of revenge from the victim.
"yaaaarrrrr, captain, i gave steve a brownbeard last night! he has no idea!" this is followed by plankwalking and "aaaars" of disapproval, or a hearty round of pirate laughter.