2 or more police vehicles moving fast in the same direction _without_ their sirens on. so named because they must be in a hurry to get cheap donuts.
(2 friends walking down a street)
1:"so I was like, yeah"
(police cars whiz by, silently)
(man comes home to his girlfriends' apartment after work)
M:"did you hear about the donut sale?"
M:"two cop cars whizzed by me on the interstate with no sirens."
F:"oh, it must have been that shooting I heard about..."