There's been some mention of the mess bar being a part of the home of those who live in. Errrm...I don't have a bar in my house. I have to leave ny home to go to a bar. Most messes have the "domestic" part which is properly de-regulated. I accept that the dining room is the exception to the rule.
Although I tend to support the relaxed dress rules, I do refute the concept that the mess bar is part of the home of those who live in. You happen to live very close to your local...and thats it.