Michael Coe, 35, stopped driving and allegedly confronted the 16-year-olds, demanding to know if they were Muslims.
When they lied and told him they were not, he grabbed the boy around the neck before throwing him to the floor.
At Southwark Crown Court Mr Coe, a Muslim, denied assault occasioning actual bodily harm and battery.
He admitted assaulting the 16-year-old boy in Wilson Road, Newham, on 15 April but claims it was self-defence.
The boy, who cannot be named for legal reasons, told the court he was hugging his girlfriend goodbye when Mr Coe shouted "let that little schoolgirl go".
He said Mr Coe grabbed him by the throat, causing him to black out.
He said: "I woke up - there was blood on my hands and I could feel blood on my face, my head was throbbing and I was very dizzy and also felt sick."
The court heard schoolteacher Boutho Siwela went over to help the pair when Mr Coe also allegedly attacked him.
Prosecutor Jonathan Polnay told the jury: "This case is about what started as unpleasant bullying with religious overtones in the street, followed by an attack by this 35-year-old man on a 16-year-old schoolboy.
"This was completely unpleasant and utterly unwarranted - this is a grown man on a child."

Pensions currently rise by the highest of inflation, average earnings or 2.5%.
There have been warnings over the cost of the lock, and the government says it will review it after 2020.
Shadow Treasury minister Rebecca Long-Bailey said this caused "uncertainty and worry", pledging to protect it "throughout the lifetime of the next Parliament", due to end in 2025.
Speaking during Treasury questions in the Commons, Chancellor Philip Hammond said it was responsible for the government to decide which commitments it can afford to keep at a spending review before the end of Parliament.
Attacking Labour's pledge, he added: "I think it tells us everything we need to know about the Opposition - that three-and-a-half years out they're willing to spray around commitments without any idea of what it's going to cost them."
During last week's Autumn Statement Mr Hammond said the triple lock would be maintained until 2020 but suggested it would then be reviewed.
There have been calls for it to be scrapped, including from former pensions minister Baroness Altmann, who said the costs would become "enormous" after 2020, and the previous work and pensions secretary, Stephen Crabb.
Speaking after Treasury Questions, shadow chancellor John McDonnell accused the Conservatives of "abandoning older people" by not guaranteeing to continue the pledge.
He added: "Labour will support the pensions triple lock and instead of cutting taxes for the super-rich and giant corporations will make sure our NHS and social care is properly funded."

The Nikkei 225 closed up 50.80 points at 20,650.92, its fifth gain in a row, having risen by 4.4% over the week.
The market was lifted as the yen remained weak against the dollar, which is considered good news for exporters.
In mainland China, stocks rose with the Shanghai Composite climbing 3.5% to 3,957.35.
In Hong Kong, the Hang Seng index closed 1% higher at 25,415.27.
In South Korea, shareholders of construction firm Samsung C&T have approved the merger plans with holding company Cheil Industries.
The deal had been strongly criticised by US hedge fund Elliott Associates, the third-largest shareholder in Samsung C&T.
The share prices of both firms dived after the vote, with Samsung C&T closing down 10.4% and Cheil dropping 7.7%.
The country's benchmark Kospi index closed down 0.5% at 2,076.79.
In Australia, the S&P/ASX 200 index ended flat at 5,670.11.
But Evan Lucas, market strategist with IG, said in a note that he was optimistic about the general outlook for Australian stocks.
"China worries have died down and Greece is now a non-issue (until September, anyway). The next month or two may be the first positive months since February."
A "bully" grabbed a schoolboy by the throat and called a teenage girl a "whore" after spotting them cuddling in east London, a court has heard.
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Labour says it will keep the "triple lock" protecting the state pension throughout the next Parliament.
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Japan's Nikkei index registered its biggest weekly gain since October, while Asian shares were mostly higher as worries over Greece and China eased.