If a non-pilot was to obtain a captains uniform and go to a fancy dress party, that's one thing, amusing and harmless fun ... if he/she was to wear the same uniform and hang around the local airport, some may interpret that as an attempt to deceive, and most normal people out of an abundance of caution would probably not elect to wear that particular garb in those circumstances. Nothing illegal, but I would question the persons intentions.
If I owned a set of RAF wings given to me by a friend and I was wandering around an airfield in green overalls, I would not wear them, as i would not want people to get the wrong impression ...