David Osborne walked into the Stag and Pheasant pub, on Clumber Street, and hit the manager while he was cleaning cutlery, at 3.30pm, on September 19.
Osborne shouted: “You must know what this is about.”
The manager saw him approach with his right fist clenched and a tussle ensued, said prosecutor Robert Carr.
Both men ended up on the floor and other customers helped separate them.
He was last in court for assault occasioning actual bodily harm, in Cardiff, in April 2008.
Harry Bevan, mitigating, said Osborne was a regular customer at the pub, who had been walking home a few weeks earlier when he helped a 17-year-old girl who was in distress, and waited with her until police arrived.
“Over the next few weeks rumours began to circulate that he has an interest in young females - which he doesn’t,” Mr Bevan said. “He chose to confront the manager.”
Osborne, 32, of Frederick Street, admitted common assault, when he appeared at Mansfield Magistrates Court, on Friday.
Chair Richard Eaton said: “The appropriate course of action is not to walk up to someone and simply assault them, which is what you did here.”
He was fined £80, and was ordered to pay a £30 government surcharge and £50 compensation.