Its just accepted practice. If you spot a fellow Pilot at the local shops getting a coffee in uniform you have a bit of a chuckle.
The worst offenders are generally SPLs, hell I saw a WAAC student at a nightclub in Perth years ago in full uniform on the dance floor, (around 2005??) I think the pictures may have been posted on here
The only time the uniform is fair game is commuting to and from work, some guys even remove the insignia as soon as they log off at shifts end.