I light up infront of cops all the time, they just don't care. 420 on the hill in Ottawa, 1500 people smoking pot infront of the parliament buildings and not a damn thing the cops could do about it.

I was on a bus going downtown for Canada day, blazed out of my mind before hand, and as usual, people started lighting up on the bus. The police got on on the next stop and said, "Listen, guys, if you're going to smoke a joint, do it downtown, not on the bus, you don't want the bus driver getting high do you?" Everyone respected his wishes, but of course, some dumb ass responded, "Yeahhh!!!" And the cop hauled his ass off the bus, and we all continued on our way.