Quote Originally Posted by Jordan View Post
Sorry to be misleading I was only trying to supply additional information for any civvies who would be invited to a military dining in night for any reason.

Jordan
I thought, possibly erroneously, that "dining out" implied guests attending the mess, whilst "dining in" implied only members of the mess would be present.

Either way it doesn't matter-- you are absolutely right: if one is a guest one should always strive to be dressed properly. In this instance (a military mess night), the waistcoat should be considered an absolute requirement.