In boxing jargon, a palooka is an unsuccessful boxer, someone who always or almost always loses. If you want to pad your won-loss record, you ask your trainer to sign you up to fight against some palookas.
My dictionary says that the origin of the word “palooka” is unknown. Are there any theories about it? It sounds like it may be a loan word from some foreign language (the way the Spanish vaquero was turned into the English buckaroo). Or it may just be a made-up word.
While the expression predated the the poplular comic strip Joe Palooka, I think most would agree that the comic strip syndacated by King Features (about a sometimes retired boxer who solved crimes, fought spies and handled domestic problems) for much of the 20th century did popularize the expression and brought it into the common culture as opposed to remaining just a boxing expression.
FWIW, the comic stirp also spawned a series of “B” movies in the 1930s or early '40s about Joe Palooka.
“It wasn’t him, Charley, it was you. Remember that night in the Garden you came down to my dressing room
and you said, “Kid, this ain’t your night. We’re going for the price on Wilson.” You remember that? “This
ain’t your night”! My night! I coulda taken Wilson apart! So what happens? He gets the title shot outdoors
on the ballpark and what do I get? A one-way ticket to Palooka-ville! You was my brother, Charley, you shoulda looked out for me a little bit. You
shoulda taken care of me just a little bit so I wouldn’t have to take them dives for the short-end money.”
Marlon Brando, as Terry Malloy in On the Waterfront.
By the way, I coulda had class, I coulda been a contender.