Darren Pidgeon, 29, required skin grafts to repair third degree burns to his face and body.
Basildon Crown Court heard there was "no obvious reason" for the attack in Thundersley, Essex, in June 2014.
Ashley Russell, 30, of Basildon, and Christina Storey, 32, of Rayleigh, each deny throwing a corrosive liquid.
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Opening the trial, prosecutor Greg Unwin said Mr Pidgeon had stopped at traffic lights when he noticed a red Rover, driven by Ms Storey, pulling alongside him.
As he pulled away, the Rover drove in front of him although it was not a "near miss", he said.
Mr Pidgeon then drove into Kingsmere, a residential cul-de-sac, to turn around and as he went to reverse a car pulled in behind him.
"He was essentially trapped, blocked in by this other vehicle," said Mr Unwin.
"The prosecution say this is the same car. A passenger of the red car then got out and ran round to Mr Pidgeon's door, where he had the window wound down, and he said words to the effect of 'have you got a problem?'"
It is alleged Mr Russell then sprayed the victim in the face and also punched him in the head.
"Darren Pidgeon was in excruciating agony, his eye was watering, some of the substance had gone into one ear," said Mr Unwin.
"He was confused and disorientated. Mr Pidgeon has no idea why he was attacked.
"As the liquid started to burn into his skin in his face, his arm and the side of his body, he screamed in agony."
Residents gave him water to wash his eyes before ambulance crews and police arrived moments later.
Tests showed the acid had a pH level of one, indicating "extreme acid".
Ms Storey also denies aiding and abetting an offender.
The trial continues.
A man was left in "excruciating agony" with serious chemical burns when a stranger sprayed acid at him though his car window, a court has heard.