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go bananas
Act crazy, as in "When it comes to animal rights, some people go bananas." According to the lexicographer J. E. Lighter, this expression may allude to the similar "go ape," in that apes and other primates are closely associated with eating bananas.
Slang; second half of 1900s
Source: The American Heritage® Dictionary of Idioms by Christine Ammer.
Synonyms:
babble, be delirious, carry on, come unglued, come unzipped, freak out, fume, gabble, go ape, go bananas, go crazy, go mad, harangue, jabber, perorate, prate, prattle, rage, rail, rant, rattle on, roar, run amuck, splutter, storm, talk wildly, thunder