A scribbled note found next to a dead body has led to a Victorian man becoming the first person in the state jailed twice for manslaughter.

Kenneth Patrick Mahoney, 52, pleaded guilty to manslaughter after he hit David Tweedly twice on a St Kilda street in October 2017.

He attacked Mr Tweedly after a "perceived slight" and hit him twice for no reason, Justice John Champion said during his sentencing remarks in the Supreme Court.

The second "haymaker" punch knocked Mr Tweedly to the ground and Mahoney threw his arms up in an "apparent celebration", Justice Champion said on Wednesday.

The victim managed to get up after the attack and make his way to a chemist before returning to his room at a boarding house.