“…be polite and professional, but know what it takes to look — and be, if necessary — dangerous in the eyes of the criminal predator.” – Sgt. Steve “Pappy” Papenfuhs via Be dangerous: Maintaining street smarts off duty.
Good advice that carries over to the average guy walking the street. A friend/mentor said to me years ago, “If you act like a wounded minnow, you’ll be treated like one.” Same point as mentioned above, just a different expression. It’s a worthwhile read.