Originally Posted by Nervous Jock
I always like the nickname "The Andrew" for the senior service

And 'Crabs' for the other lot, chocks awah!
Are you referring to "Crab Fats", as applied to the "Puss"(a name commonly used to refer to the Navy) (Royal Navy term, abbrievated for Pusser, as in a ships Purchasing officer - pusser...)

Another more plausible explanation as to why the RN refer to the RAF as 'crabs' goes back to the days of rum, sodomy and the lash (about last week in fact). One of the more unsavoury aspects of the average matelot was his unfortunate habit of contracting pubic lice or "crabs" during his shore leave. The treatment for this condition was to get a chum or shipmate to apply a liberal application of a greasy blue/grey ointment (known affectionately as "crab fat") to the affected area. The proper name for the ointment was Blue Unction.

While some of the explanations below are derived from or purported to be the "official" version the RAF have been named "crabs" due to the fact that they have no limit to the number of sideways paces they can do as a drill movement. While army and navy have a fixed limit of sideways paces the RAF can actually march the entire width of a parade ground sideways.

Once upon a time, the RAF flew Spitfires with tail wheels near the tail and huge Merlin engines at the front. This meant that during taxiing, all they could see to the front was an enormous engine. In order to see what was in front of them, they had to look over the side and zigzag, thus they'd be moving sideways. On landing, they would sideslip to lose height.

Because of airfield security, the only time land-locked mortals got to see the RAF anywhere near close up was during landing, take-off and taxiing, when they were moving sideways. Since only crabs walk sideways, clearly the RAF was staffed by crabs.

Coupled with the fact that the Fleet Air Arm attracted all the best pilots and the Army always won inter-service regattas, a once popular forces T-shirt logo read: 'Fly Navy.Sail Army. Walk Sideways!'