Public relations professionals are supposed to demonstrate creativity, restrained by good judgment. That should be reflected in their Halloween costumes. So, here are some safe bets, costumes which can be worn to a client's party as well as for a club crawl.
A Tylenol capsule
Pair of Boxers wearing name tags "Jack O'Dwyer" and "PRSA"
Sandwich board listing all the categories from Edelman's no-trust survey
Bob Dilenschneider mask, attached to a male Millennial hard body
Twitter Blue Bird
Steve Jobs in God attire, related paraphernalia
JFK as Geezer he would have been now
Dick Cheney's mechanical heart
Don Draper mask, wearing nametag "Now PR guy since BigData killed ad biz"