Keane, 43, denied the public order offence after cabbie Fateh Kerar, 44, had told him to “cheer up” and smile.
The Old Trafford legend gave evidence from the witness box himself and, after a half-day trial at Manchester Magistrates’ Court, he was cleared.
District Judge Duncan Birrell said there was something of the “thwarted fan” about Mr Kerar and Keane’s lawyer described the whole incident as a “storm in a teacup”.
Keane was cleared of causing harassment, alarm or distress to Mr Kerar. Dismissing the case against Keane, the judge told him: “I have listened with great care to the evidence in your case. The burden of proof is on the prosecution.
“It’s my view, taking as I have said a careful account of the evidence, that they have failed to discharge their burden; therefore I find you not guilty.”
He added that the evidence was “riddled with inconsistencies and improbabilities”.
He told Keane: “You probably will regret getting out of the car.”
The defendant gave no reaction as the verdict was given.
Keane told the court he did not flick a “V” sign at Mr Kerar who had accused him of swearing and staring at him in Altrincham, Cheshire, on the morning of 30 January this year. Football fan Mr Kerar told the court “I love Roy Keane”, but claimed the Old Trafford legend, now the assistant manager of the Republic of Ireland, gave him “bad looks”.
Mr Kerar said Keane later followed him in his car before flicking the V sign then getting out of his black Land Rover and approaching the cab, swearing.
But the former Ipswich and Sunderland manager denied any wrongdoing.
Keane said he was “chilling out, relaxing” in his car waiting for his wife when he noticed Mr Kerar across the road in his taxi.
Keane said they nodded to acknowledge each other but as they both moved off in their cars, the cabbie made a gesture.
Keane, pushing the corners of his mouth up with his fingers, told the court: “He gave me a smirking gesture.” As Keane and his wife passed in his car, the witness said Mr Kerar gave him a “fake smirk” but he did not react.
He added: “I noticed in our mirror that the driver gave me two fingers.”
At a junction, Keane said he then got out of his car.
“I opened the door and literally asked him what’s his problem. I said it two or three times. He said something like, ‘You need to cheer up’, along them lines.
“I turned and got back in my car. With my back to him, I said, ‘Oh f*** off’.”
Stuart Denney QC, defending, asked the witness: “Anything to be aggressive with at the world that morning?” Keane, with a short laugh, replied: “No. Not that morning.”