off one's rocker

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off one's rocker

1. (slang) Crazy; insane.

   He's off his rocker if he thinks he can tackle the whole thing alone.

   • 1960, P[elham] G[renville] Wodehouse, chapter VIII, in Jeeves in the Offing, London: Herbert Jenkins, →OCLC, page 86:

     “Bertie! Your manner is strange.”
     “Your manner would be strange if you'd been sitting on the floor of Wilbert Cream's sleeping apartment with a chair round your neck, and Ma Cream had come in.”
     “Golly! Did she?”
     “In person.”
     “What did you say?”
     “I said I was looking for a mouse.”
     “Couldn't you think of anything better than that?”
     “No.”
     “And how did it all come out in the end?”
     “I melted away, leaving her plainly convinced that I was off my rocker.”

• A group is commonly qualified with a singular ("they're off their rocker") but sometimes also a plural ("they're off their rockers").