Stuart Fry claimed he was provoked when he attacked Glen Paton outside a pub in Pumpherston, West Lothian, leaving him bleeding from a four inch face wound.
Livingston Sheriff Court heard Mr Paton had approached Fry after he went into the pub.
He told the accused, who was out on licence from a life sentence for murder: "You shouldn't be in here. I know what you've done... get out!"
Fry was jailed in March 2002 for strangling Jean Moore, 36.
Sentencing Fry, Sheriff Susan Craig told him: "I accept this was a circumstance where you were provoked into acting in the way you did."