At a set of traffic lights locally, a queue of cars had built up behind a learner driver who kept stalling the engine. The other drivers were getting impatient and hooting their horns.
However, the car behind the learner contained members of the constabulary and, after the lights had changed a couple of times with no movement, the police driver turned on his loudspeakers and asked the drivers behind him to be patient, pointing out that 'we've all had to learn'.
Then the learner driver got the car in gear and moved off.
Into the police car.
Then the queue heard over the loudspeaker, 'Bloody stupid cow'!