The young autistic man who was apparently the target of an expletive-filled tirade from an Ottawa bus driver says he was reading from a script he had written when the driver lashed out at him.

Matthew Taronno, a 20-year-old who describes himself as "mildly autistic," said the script contained some "inappropriate language" and said he went to the front of the bus to apologize. The driver was in no mood to hear it, Taronno told CBC News on Sunday at Algonquin College, where he is studying script writing.

The 55-second cellphone video of the exchange, shot on the No. 96 bus from downtown Ottawa to Kanata, has attracted hundreds of views and many angry comments since it was posted to YouTube.

It shows a young man in shorts standing near the front of the bus when, out of view, another man, apparently the driver, yells at the passenger.

"Shut the f---k up!" the older man says to the passenger. "Shut your ignorant f---king cake-hole! Don't say another f---king word!"

The stream of abuse includes a physical threat against the rider.

"If you don't shut your f---king face I'm going to stick my fist in it!"

As the bus stops at the Eagleson Park and Ride, the young man wheels around and runs out the back door, saying "Sorry" as he goes.

Only 2 passengers on bus

The person who shot and posted the video said the young man had been talking loudly into a cellphone before he walked to the front of the bus, seemingly enraging the driver.

He added Taronno was also repeatedly ringing the bell to get off the bus. Taronno said he regretted reading aloud but said the driver was in the wrong, too.

"I know what I did may have offended him and I regret my action and I understand what I did was wrong even though I was saying that for my screenplay and it still may have come off as offensive and I regret that," said Taronno.

"But … he needs to have a consequence for his action for him to understand what he did was wrong," he said.

The video drew strong reactions from Ottawa mayor Jim Watson, who said Monday the video made him angry.

"I don't want to prejudge the outcome but that kind of language is hurtful and it made me angry quite frankly when I saw it because we are trying to do our best to change the image of OC Transpo and we take one step forward and two giant leaps backward," said Watson.

OC Transpo chief Alain Mercier apologized to Taronno and confirmed an investigation is underway. He said "appropriate actions" will be taken.

"Customer relations is always a priority for us and we take this situation very seriously," said Mercier, who added that any action taken against the driver will be kept confidential.

Video inconclusive, union says

Garry Queale, president of Amalgamated Transit Union Local 279, said it is unclear from the video whether the person screaming at the passenger is the driver.

"Well there is no sign of any driver being shown," said Queale. "There is a passenger standing beside the driver's area … from what I have seen it could be a person sitting over across yelling at somebody."

Queale said if it was a driver, it is also unclear from the video what set him off and said any investigation should probe the circumstances leading up to the apparent tirade.

The embedded YouTube video caption incorrectly refers to Taronno as being "mentally ill." He has since clarified that he is "mildly autistic" and not mentally ill.