A dngerous driver who admitted having smoked "a bit of weed" when arrested refused to provide a breath sample, saying: "How do I know he's a doctor?"
Henry Cahill (20) had been stopped for driving erratically at high speed and performing "skids" when gardai smelled and discovered cannabis in his car.
Judge Michael Walsh jailed him for six months and banned him from driving for six years.
Cahill, of Conroy Park, Kilcullen, Co Kildare, pleaded guilty to dangerous and uninsured driving as well as refusing to provide a sample.
He also admitted driving without a licence and possession of cannabis.
Dublin District Court heard that on August 11 gardai were called to Le Fanu Road, Ballyfermot, where a red Mazda was being driven at high speed in a green area and "performing some kind of skids".
The car went through a red light and mounted the footpath, where it was driven erratically, a garda told the court.
The car was stopped and the driver, Cahill, was arrested.
Gardai noticed a smell of cannabis coming from him, and when asked about this he said: "I smoked a bit of weed today."
A small amount of cannabis was found under the driver's seat and the accused was taken to the local garda station where a doctor was called to take a sample.
When asked to provide a sample, Cahill said: "How do I know he's a doctor? He ain't coming near me."
Cahill had a large number of previous convictions including three for driving without insurance. He accepted he had a "terrible record for such a young man", his lawyer said.
His teenage years were "plagued by drug use", but he detoxed in prison and was now drug-free.
His lawyer asked Judge Walsh to be as lenient as poss-ible given that Cahill had addressed the root cause of his offending, and not to add to a sentence that he was already serving.
The car he was driving had since been sold and he realised he would be sentenced to a lengthy driving ban.
Judge Walsh said it was fortunate that nobody was injured as the incident happened in a densely populated area with young children around.