Having been both a Battalion Adjutant and the PMC of the Home Station Mess (when there still was such a thing...) I have had some dealings with the issue of proper dress in the Mess. Having lived the first six months of my present posting in the officer shack at Kapyong, and having taken my meals in the Combined Mess, I have some familiarity with dress in dining facilities.
First of all, I think we are being rather myopic to think that common daily practices in the military never change, or that if they change this will somehow bring about THE END OF THE ARMY AS WE KNOW IT. Rubbish. Let me illustrate.
When I joined 3 PPCLI as a new subbie in 1983, we were forbidden to bring women into the bar area of the Mess. Forbidden, plain and simple. I let my wife into the bar once during a mixed dining-in to use the phone to call home in an emergency and was taken aside afterwards by the Senior Sub and admonished never to do it again. This silly practice was solemnly described as "tradition". Needless to say, it has not survived. As well, we were required to "dress up" for every evening meal, usually in jacket and tie. We were not to wear uniform of the day unless we were the BOO or had night training. This "tradition" IMHO reflected a legacy of the lifestyle of the upper-class Victorian gentlemen who made up the Officer Corps from which we inherited many of our attitudes and traditions. Tangentially, this included a mindset that was, IMHO, anti-professional in the extreme and regarded social prowess as being at least as important as any demonstration of military knowledge or skill. This practice has also faded away, and I do not miss it.
My point then, is that common daily practices in the military are constantly evolving and changing, as are tactics, policies, equipmen and everything else about our profession. In the midst of all this change, we do well to hold onto certain important anchors such as respect for military history especially examples of bravery and sacrifice, respect for and practice of military virtues such as loyalty, honour and personal courage, and adherence to a commonly understood code of ethical professional behaviour. At the same time, we waste our time and energy worrying about why nobody wears flannels to supper anymore. Well, we don't wear a Sam Browne to the office either, we don't force soldiers to be Mess servants, and we officers don't have batmen anymore. Change happens, all the time.
Are we worse off because we let a soldier wear a clean T-shirt and jeans to eat his supper? IMHO, probably not. I submit that the old Canadian Army that fixated so much on these issues was a far less operationally focused, far less ethical, and generally less professional Army than we are today. Now, before I am assaulted by the flannel-wavers, look up professionalism as we currently define it in our Army. (Chapter 1, page 6, Duty With Honour). Having served 30 years in this Army of ours, I submit that we are far closer today to meeting that definition than we ever were back in the days of RSMs measuring trouser cuff lengths at the barrack gate. Fire away. Cheers.