Tatenda Kamosho, 19, was poisoned after a bite wound turned septic.
Kamosho was also stabbed in the arm in the assault, which left him with the hallucinating psychosis.
Northampton Crown Court heard that Jordace Sinclair, 18, carried out the attack on Kamosho in a McDonald’s restaurant.
Prosecutor Mary Loram told how Kamosho’s condition deteriorated to such an extent following the attack, that he believed he was Barack Obama and could hear “six million people talking, with God-like delusion,” the Sun reported.
The court heard that Kamosho is still being treated at a psychiatric hospital, and is yet to make a full recovery four months later.
Loram said Sinclair attacked Kamosho in the fast-food eatery in Northampton - and stabbed him so hard that his knife snapped in two.
“There was an exchange of punches. It then looked as if it was going to die down,” she said.
“The two then fell over and the defendant then bit him to the cheek area and had to be pulled off by the staff,” she added.
Despite being treated and released from hospital, Kamosho had to be re-admitted the next day when his airways closed and he was put in a five-day induced coma.
By June 26, he started hallucinating, developed psychosis and had to be sectioned under the Mental Health Act 1983.