Christopher Dootson, aged 22, of Mere Avenue, Leigh, threatened a man in a nightclub toilets.
He was jailed after Recorder Vincent Fraser, told him: "Witnesses must not be subjected to threats, particularly of physical violence."
Dootson was found guilty of witness intimidation at Liverpool Crown Court.
The court heard the incident happened at Barbarellas nightclub on December 14 last year when a man, who had been assaulted by a friend of Dootson's, had gone for a night out.
Dootson was abusive towards him in the toilets and threatened to give him a "pasting", clearly referring to the court case. The man was afraid for his safety and left, but later on Dootson made obscene gestures at him and pointed at him.
Michael Morley, defending, said Dootson had no previous convictions, he had been drinking and his behaviour had been out of character.
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