411 REFERENCE · Wiktionary
I should cocoa
Reference material by Wiktionary contributors. This retains its source identity and is not 411 news reporting.
English
Etymology
Rhyming slang, possibly using cocoa drink for think. Another possibility is that it is taken as a rhyme with say so.
Interjection
en Cockney rhyming slang British dated humorous I should say so; I should concur; I strongly agree en almost always used ironically or sarcastically.