So I believe the first time I've come across the word "Deculture" was during the first Human-Zentran war (The Original Macross series). The Zentraedi used the word "Deculture" generally for phrases like "Impossible", "Unthinkable", "Unimaginable" or "Unbelievable". The word also had a different meaning if prefixed with the word "Yakk" as in "Yakk Deculture" meaning "Deplorable", "Disgraceful", "Disgusting".
You'll find that later on in the Macross Universe, "Deculture" becomes a Zentradi slang word for the phrase "no way" (disbelief); for example, say I go to a concert and the band's final