while there may be situations that it would be o.k. In the parameters of the O.P. question i assume the rider would be in the same lane as the car.
in that case it's an a-hole move, wait your turn like everyone else. to those that say they are helping traffic flow, i say bull. if that's the case lets all drive however and wherever we think is best. I can't believe how self important some of you think you are.
oh wait, didn't some riders try that just recently in new york?!