off your nana
off (one's) nana
old-fashioned slang Crazy, insane, or mentally deranged. Sometimes written as "off (one's) 'nana" to reflect the abbreviation of "banana." I think you've gone off your nana for giving up that cushy office job, but, hey, follow your dreams. Don't go off your 'nana, I only took the car out for a quick spin. My auntie likes to let people think she's off her nana, but she's actually incredibly clever and witty.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
off your nana
mentally deranged. AustralianNana in these idioms is probably short for banana ; compare with go bananas at banana.
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