I should cocoa

I should cocoa!

dated No way; there's no chance; you must be joking; I think not. From rhyming slang of the sarcastic phrase "I should say so," meaning the same. Primarily heard in UK. Bob: "So, are you going to finally join us for some karaoke?" Janet: "I should cocoa!"
See also: should
Farlex Dictionary of Idioms.

I should cocoa (or coco)

I should say so. British rhyming slang
1996 Melvin Burgess Junk He said, ‘Someone'll really buy it and it'll be theirs then.’ ‘I should coco,’ I said.
See also: cocoa, should
Farlex Partner Idioms Dictionary
See also:
  • cocoa
  • I should cocoa!
  • iron poof
  • have a Captain Cook
  • donkey's ears
  • bag of fruit
  • brassic lint
  • ginger beer
  • Brahms and Liszt
  • half-inch