A Hastings teenager has been found guilty of intending to cause grievous bodily harm to an acquaintance he set alight after dousing him with petrol, in what the Crown said was a "cynical, callous piece of bullying".

The verdict was delivered to Matt-Dillion Shannon in the Napier High Court this afternoon. Shannon had pleaded guilty to a charge of causing grievous bodily harm with careless disregard at the start of his trial on Monday.

The jury of seven men and five women took four hours to reach their verdict.

While the Crown and defence agreed Shannon's actions caused very serious harm to his victim, the defence argued he had not intended to cause such harm.

Justice Christopher Allan said in order to prove the charge the Crown needed to establish that Shannon intended to cause really serious harm when he poured the petrol on his victim. If the jury believed Shannin had intended some harm, but not serious harm, it would not be enough to convict him.

Shannon, now 18, was celebrating his 17th birthday at a party in his house on August 12 last year.

Shortly after midnight he poured petrol over a 16-year-old and set him alight with a cigarette lighter as three others held the victim down.

The victim suffered severe burns to his back, neck and one side of his face. He stripped off his burning T-shirt and rode his bicycle home before being taken to hospital and the intensive care unit.

Shannon claimed to have been copying a stunt he had seen on a Jackass movie.

Shannon's lawyer Bill Calver told the jury that Shannon was a drunk, testosterone-driven young man who behaved like someone "a few sandwiches short of a picnic", but there was no way he meant his victim to suffer the serious injuries he did.

The Crown and the victim said Shannon, who worked in a service station at the time, poured the petrol from a 10-litre container. Shannon said he poured it from a shot glass and used no more than 10 millilitres.

The victim, now 17, said he was held down for about 20 seconds. Shannon says it was no longer than five seconds.

In his closing address yesterday, Shannon's lawyer, Bill Calver, said Shannon's actions were "unbelievably stupid, totally reckless, utterly moronic and extremely dangerous", but "you're dealing with a very young man who unfortunately doesn't have a great deal of wisdom".

Crown prosecutor Russell Collins described Shannon's claims as "hopeless" and said stupidity was "not a cleanser or absolver".

He said Shannon targeted the vulnerable victim in a "cynical, callous piece of bullying" and then lied to police about the boy being drunk and vomiting in a bid to provide a motive other than bullying.

He said Shannon's intention was obvious. "You pour petrol - you're a service station attendant - on someone held down, and set fire to them and then do nothing to set him free. You can have intended nothing else, " Mr Collins said.

Earlier yesterday Shannon took the stand and said the victim should have "stopped, dropped and rolled", and he would have been all right.

"I thought he'd wake up, get a fright and roll about until the flame was extinguished and he'd be fine. He just jumped up and ran around.

"If he'd stopped, dropped and rolled, it would have just been a joke instead of a serious incident."

He said others were yelling "do it" and "light him on fire".

He will be sentenced on both charges on October 15.