Its all a bit naff though isn't it?
When I was in, I wore my mess undress to a few civvy functions, but looking back I cringe a little bit at the thought.
That's not to say I wasn't proud of what I did for a living... Just that it sort of says "look at me, I need to wear this to make me interesting".
Up to you of course, but personally I think a smart dinner suit with a black waistcoat and a properly tied bow tie looks a lot smarter. Especially if you have a fat bottom like me.