A drunken reveller randomly punched an accountant in the street, breaking his jaw.
The 30-year-old victim ended up in hospital, where he had an operation to have two titanium plates inserted into his lower jaw.
Matthew Webb (22) admitted inflicting grievous bodily harm on the night of August 4 last year.
He was given a 12-month jail sentence, suspended for one year, with 100 hours of unpaid work.
Leicester Crown Court was told he had been drinking heavily with a friend.
He believed his drink may also have been spiked with ketamine, said his barrister, James Varley.
David Allan, prosecuting, said the incident happened in Belvoir Street, in the city centre, at 11.50pm.
He said: "The defendant was walking along with an arrogant attitude.
"He punched the victim in the face as he was passing.
"The defendant said nothing and just looked at him.
"It was completely unprovoked.
"Witnesses saw the defendant smirking as he skipped backwards a few steps, like a boxer expecting a reaction."
The victim, who did not at first realise how badly he was injured, pointed the defendant out to two police officers.
They spoke to Webb, who appeared "very drunk" but gave them his details.
Mr Allan said Webb also went to hospital at 2.10am that day complaining of feeling unwell and saying he might have taken ketamine. He was later sent home.
Webb, of Hattern Avenue, Stocking Farm, Leicester, was arrested a few days later.
Judge Michael Pert QC told him: "You broke a man's jaw.
"It's an illustration of the dangers of excessive alcohol leading to late-night violence in the city centre."
Mr Varley, in mitigation, said Webb was "of previous good character and had a good upbringing".
Mr Varley said: "A number of people have come to court to support him. References speak well of him. He had everything going for him and he's made a stupid mistake.
"He was out celebrating the birth of his daughter and drank far more than normal.
"On the night, he was so drunk he went to hospital because he was so out of it.
"He maintains his drink was spiked with ketamine and he can't recall anything of that night."
