be dumber than a bag of hammers
To be exceptionally foolish, dimwitted, or unintelligent. You thought you could fix the washing machine on your own, so you just started pulling it apart? I swear, sometimes you can be dumber than a bag of hammers, Larry. I used to think that she was dumber than a bag of hammers when we were kids, but she grew up to be a physicist. Are you dumber than a bag of hammers? Why would you touch the alarm when the sign clearly says "DO NOT TOUCH" in bold red letters?
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