Green’s Dictionary of Slang

1. (orig. US) a contemptible individual.

1934		H. Roth Call It Sleep (1977) 210: He’s a louser! He hits!
1939		‘Flann O’Brien’ At Swim-Two-Birds 75: Get back to hell to your prairies, says he, you pack of lousers.
1961		T. Murphy Whistle in the Dark Act I: The lousers must have stayed on for another one at The Lion.
1975		J. Ryan Remembering How We Stood 136: Mrs Clougherty [...] gave them a last look as much as to say ‘shut up you lousers’ and made straight for the hall door.
1989		H. Leonard Out After Dark 89: I knew that if I acted the mean louser and did a bunk he’d feel sorry for you.
1996		(con. 1970) G. Moxley Danti-Dan in McGuinness Dazzling Dark II iii: A dirty louser, that’s all he is.
2000		F. Mac Anna Cartoon City 269: The woman swiped at Pat with her handbag. ‘You louser,’ she yelled.

2. (Aus.) a petty thief.

1948

K.S. Prichard Golden Miles 27: A louser’s always suspected of pimping for the boss, as you know.