Speaking as a 'liver-out', I don't make a great deal of use of the Mess, but I have to take issue of a previous comment:
once it has slipped, it is nigh on impossible to recover the situation
Not true in my experience. We had a situation where the scruffs' bar was being used entirely with virtually no-one in the main bar. On several occasions, guests coming into the Mess (including visiting senior officers from other units) inevitably drifted next door. The view was that as this was their choice, so they should not be offended by what they found. However, it was not deemed acceptable by the powers that be, and the Scruffs' Bar was closed. Now we have the one bar, with reasonably relaxed sandards (trousers and a collared shirt, no logos, no sports shirts etc), with the traffic-light system. IMO,it works reasonably well, without forcing people away from the bar to the 'all ranks facility'. It needs strong but reasonable leadership, and an acceptance by the Mess Members that certain standards are not negotiable.
One other thing that made me chuckle was the Wg Cdr's statement that he expected his officers to dress reasonably at all times; no reason why people shouldn't wander round dressed as Goths or whatever, but don't be surprised if it is reflected in your OJAR!