When we shoot night exteriors in big cities, it's customary to have a cop dedicated to the set. The officer's role is to make sure nothing negative occurs between the film unit and the neigborhood. They also do some traffic control. When you shoot in dicey neigborhoods, it's reassuring to have those guys around, becasue a film shoot draws people like moths to a light, and I've seen it happen where street types begin harrassing crew members.

Last night we were shooting on Sutton St. in the greenpoint section of brooklyn. All day we'd heard forecasts of rain. sleet and hail. This made me very anxious, as I know night exteriors to be risky enough, without the water/electricity relationship, or the high winds/grip problematic (shit blows around). I'd just added a last light to a shot of an old car parked at the curb, when this cop with a thick rockaway accent says to me: "Get that light out of the street! You gotta keep a twelve foot fire lane open here."
I was rushing back to the monitor to see how our shot looked, and i stopped in my tracks, sighed, and winced.
"Sir," I said, looking at the cop finally. "You are quite seriously hampering my creative process."
I'd meant it as a joke. He didn't take it too well.
"Get your damn light outta the street." He said menacingly, "or I'll really give you something to worry about."

The funnist set-cop I've ever encountered was in L.A. We had this crusty old guy from the motorcycle division. The scene we were shooting was too sisters having the big hash out of their lives, the night before one was to get married. We were shooting on melbourne St. in Los Feliz, but it was supposed to play for Providence, Rhode Island.
As the camera rolled, these two lousy, primadonna actresses did their sisterly argument - screaming stuff like: "MOM AND DAD ALWAYS LOVED YOU MORE THAN ME! THAT'S WHY I STUDIED SO HARD AND BECAME A BIG CORPORATE LAWYER."

When the A.D. called cut, I could see other crew memebers laughing and holding their noses. The burly grey-hairedcop leaned to me and said: "Hmm. I think I'm smelling an academy on that one."