to quack like a duck. It is one of those interesting words that have two contradictory meanings. Applied to an opponent, it is abuse; applied to someone you agree with, it is praise.
George Orwell. 1984 (1949)
---
Thoughtless or formulaic speech.
text from Wiktionary, licensed under Creative Commons - Attribution - Sharealike
Ultimately it was hoped to make articulate speech issue from the larynx without involving the higher brain centres at all. This aim was frankly admitted in the Newspeak word duckspeak, meaning ‘to quack like a duck’. Like various other words in the B vocabulary, duckspeak was ambivalent in meaning. Provided that the opinions which were quacked out were orthodox ones, it implied nothing but praise, and when the Times referred to one of the orators of the Party as a doubleplusgood duckspeaker it was paying a warm and valued compliment.