Members of the Royal Air Force (including myself 25 years served!) are known as "Crabs" by members of the RN!
This is reputed to come from the first ever march past when the RAF where in their new uniforms & A senior RN officer taking the salute said words to the effect of :- "They look like crab fat"! - this was a paste issued by RN medics to clear crabs & was the same colour as the new cloth!
Skipy