The 44-year-old admitted assault occasioning actual bodily harm and two charges of possession of an offensive weapon.
Durham Crown Court heard the victim had helped eject Willis, of Lombard Place, from the pub just prior to the incident on December 24 last year.
Willis then went to his flat and returned with two candles in glass jars, which he put in socks and used to strike the man.
Martin Towers, prosecuting, said the victim, who had returned to the bar to continue drinking was struck from behind and was left covered in blood, with a two to three centimetre cut to the head.
Willis, who has 89 previous convictions, the last of which was in 2012, was given an eight month prison sentence by judge Christopher Prince.
He added: “Having been put out you were not willing to put up with what you saw as bullying. In an entirely cowardly and surreptitious fashion you went behind him and struck him on the head.”
Lorraine Mustard, mitigating, told the court Willis had been a heroin addict from the age of 20 until 2010, when he was able to kick the habit through a court-ordered treatment programme.
She said: “On December 24 Mr Willis felt he was being treated in an unfair manner, with suggestion he was dealing drugs.
“He was offended by that because any connection with drugs is behind him.
“It doesn’t justify what he did, but Mr Willis was assaulted and there is evidence he had a black eye. After he was released in the early hours of Christmas morning he had to tell his daughter he had fallen out of a tree while waiting for Santa.”
She added: “He has since seen the victim and there is no hard feelings between them. It has to some extent cleared the air because they no longer suspect him of dealing drugs.”
The man’s injuries have since healed.