William Abbott, 35, "dived on" victim Robert Young and bit him twice after the old man asked him to stop skimming beer mats across the dance floor at the Dee Club in Lochee, Dundee.
Mr Young told Dundee Sheriff Court: "I was asking him to leave the club. Somebody else came over and said to him as well.
"He turned round and jumped on me.
"He bit me on the hand then the arm."
The court heard other patrons were "horrified" by what happened.
Abbott, who had been drinking, was described as "off his nut".
Police arrived to find tables overturned, glass on the floor, and Mr Young receiving first aid.
Jurors were shown pictures of a bite injury to Mr Young's left upper arm.
Just before the violence erupted, customers had been listening to the club's vice-president Paul Neave singing the Dean Martin hit "Ain't That A Kick In The Head".
Today after a three-day trial, a jury took less than 90 minutes to find father-of-two Abbott, of Ettrick Crescent, Dundee, guilty of assaulting Mr Young to his injury in the incident at the club in
Taylor Street, Dundee on February 24th last year (2019).
Three other charges were found not proven -- that he had assaulted Mr Neave by punching him on the head; that he had recklessly thrown glasses at other customers; and that he had assaulted another man by throwing a tumbler at him, that struck him on the body.
He had denied all the charges.
Abbott said in evidence that "for some reason" he was asked to leave the club, and was just about to do so when, he claimed, Mr Neave and others forced him to the ground and beat him up.
Prosecutor Kirsten Letford said this was "simply not true".
She said Abbott had been "so aggressive and angry" in the club that he approached an 87-year-old man when he told him to stop flinging beer mats, and took his anger out on him.
After the verdicts, Paul Parker-Smith, defending, told Sheriff Alastair Carmichael that Abbott was the operations manager of a body shop in charge of a workforce of 10 men.
He said his client was "under no illusions that he had been convicted of a serious offence against an elderly gentleman".
The court heard Abbott had four previous convictions for violence, but the most recent was from 2010.
Sentence was deferred until March 16th for reports, including a restriction of liberty assessment, and bail was continued.