In principle, mess dress should only be worn to non-military events when the equivalent civilian dress is tails.
Surely that would only be true of white-tie civilian functions? The mess dress equivalent being No 5A with the exceptionally uncomfortable white waistcoat, stiff-fronted shirt and white tie?
So glad that I rarely need to wear a tie of
any description these days! The last time I attended a black tie with miniatures event, someone tried to tell me that I shouldn't have worn the premier tanker squadron's red-and-black tie. I suspect my response included curt reference to fornication and travel!