bathtub warrior

usually a marine cadet or sea cadet who thinks they're better than everyone else and thinks that they're as good as an actual soldier when in fact they actually just splash around in the water,fall off boats and fail to dry capsize.
basically the equivalent to a puddle pirate but more commando and less sea cadet...

army cadet next to a river: oh look at that bathtub warrior, that twat cant even swim!