A play-fight between best friends ended in casualty after one of the men was punched so hard he suffered a fractured eye socket.
Daniel Arnell, 24, was arrested and the close friendship between the two men is over.
His victim, Adam Aldred-Lane was due to be Arnell's best man at his wedding next summer but he is no longer going to take on the role.
At Brighton Crown Court Arnell, who works for a children's after school club, admitted inflicting grievous bodily harm.
Arnell, of Dalewood Gardens, Crawley, who has no previous convictions, was sentenced to 12 months in jail suspended for two years. He must carry out 250 hours unpaid work in the community and pay £780 costs.
The court was told the two men, who had been best friends for seven years, went out on the night of October 27 last year in Crawley and both had been drinking when they started play-fighting.
Rob Hall, prosecuting, said Arnell had hit Mr Aldred-Lane and bitten him "in banter".
He said: "Towards the end of the evening the victim was assaulted in a way that was far more serious. He has little recollection but recalls seeing a fist coming towards his face."
Mr Aldred-Lane needed surgery on his face and a metal plate inserted where his eye socket had fractured. He was left with some paralysis to his face and problems with his teeth.
Andrew Stephens, defending, said Arnell had acted out of character.
He said: "He cannot recall the offence because he was intoxicated at the time. This started as some play-fighting.
"He is deeply remorseful and ashamed. This schoolboy behaviour has come to an end. He has lost a very valuable friendship."
Judge Anthony Scott-Gall said the injury had a significant impact on the victim, who had since given up his job and gone travelling.
He said: "As the evening progressed you drunk more and more and as a result you were unable to control your stupid behaviour. You punched him so hard you flattened him.
"There was no malice intended. It was an utterly feckless punch that has ruined a friendship and blighted a young man's life."
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