Indicating a man was of illegitimate birth as his father was not and is still not married. Not to be confused with son of a bitch where bachelor is sometimes substituted for bitch. Melvile used the phrase in Typee. Not sure if he was substituting but I was struck with the subtlety.
Well sir , I will respect your mother but you are one sorry son of a bachelor.
Greeting: What’s up you motherles sons of bachelors?
Greeting: What’s up you motherles sons of bachelors?
by Wikidictionarymiki February 13, 2018
Get the son of a bachelormug.