Somebody asked me whether there was any connection between the phrase ‘paddy whacker’ and the childrens song ‘knick, knack, paddywhack’.
I think this unlikely - I can find not evidence of any connection at all.
The phrase in its most common usage is a somewhat discriminatory term referring to a machine used by builders to level the hard core or soil prior to laying a drive way, or doing building work. These machines, more correctly known as ‘compactors’ get their epithet from the ‘fact’ that many of the workers doing building work and driveways were of Irish origin; ‘Paddy’ being a generic, and slighty derogatory, term to describe all Irish men.
I as also found some evidence to support the theory that the ‘whacker’ part is NOT related to the ‘whacking’ that the plate does, but instead comes from the English pronunciation of a German company name that produced many of the early models. You can make your own mind up on that one. All I will say is that even construction equipment manufacturers have some cunning marketing skills, and this may be behind this myth.