I did this a few years ago as a last-minute, no notice costume. Just threw on slacks, white shirt and tie, a bike helmet, and a backpack. We hit the bars later that night and some drunk dude wanted to fight me because he thought I was actually there to try and convert people or something, even though it was Halloween, everyone was dresses up, plus I was drunk and wielding two full beers at that particular moment.
I just handed him one and said "pay lay ale brother dude, see you in priesthood tomorrow." Cheersed him, then chugged the other beer and walked away while he still tried to figure out what had just happened. That was a great night...
It was less fun than I anticipated - mostly because I think people seemed uncomfortable. I probably should gone all out and told people it was for the musical. I probably could have channeled Josh Gad. :)