Mayor Bill de Blasio has been in office barely a year, and already forces of entropy are roaming the streets, turning their backs on the law, defying civil authority and trying to unravel the social fabric.

No, not squeegee-men or turnstile-jumpers. We’re talking about the cops.

For the second straight week, police officers across the city have all but stopped writing tickets and severely cut down the number of arrests. The Times reported that in the week ending Sunday, only 347 criminal summonses were issued citywide, down from 4,077 over the same period last year. Parking and traffic tickets were down by more than 90 percent. In Coney Island, ticketing and summonses fell to zero.

The city has been placed in an absurd position, with its police commissioner, William Bratton — a pioneer of “broken windows” policing who has just written a long, impassioned defense of that strategy as an essential crime-fighting tool — leading a force that is refusing to carry it out.

Police union officials deny responsibility for the mass inaction. But Edward Mullins, president of the Sergeants Benevolent Association, said officers had talked among themselves and “it became contagious,” apparently like the flu.