A bit of logic to the original title...

I think we can all agree that the reason Leone gave for calling the film Duck, You Sucker! is bollocks. Nobody says that. Ever.

But there's precedent for laboured, pun-ish titles that kind of sound like vernacular in places that you would not be surprised were an inspiration for Leone, in this film as well as his earlier ones.

The Looney Tunes and Merrie Melodies shorts of the golden age were, I think, a strong influence on the banter between John Mallory and Juan Miranda. The scene were Mallory tricks Miranda into a suicide mission against is pure Bugs and Daffy.

Duck, You Sucker! Could easily be a cartoon where Bugs and Daffy visit Transylvannia (again). 

Glasgow's FOREMOST authority Italics = irony. Infer the opposite please.