Derogatory
reference to a
United States Marine. Commonly a reference to a member of "MARDET", the Marine Detatchment that is present on some Navy ships. MARDET personnel perform duties as sentries, security, orderlies, provide an honor guard for special occasions, and provide the nucleus of the ship's
landing party among other things.
Sea duty is one of the oldes traditions of the Corps, so this is a good epithet for starting a fight with any Marine (not just MARDET), esp. if said with plenty of sarcasm. Bring your own trauma surgeon.