Somebody who claims to know everything about warships and naval warfare, but actually has little to no real world experience in the field. The naval equivalent of the Armchair General.
There he goes, hating on the Zumwalt destroyers again. He's such a BathtubSkipper.
Pajama casual is a term used when working from home and preparing for a video conference. All business above the waist and your pajama pants down below.