be one egg short of an omelet
derogatory To be unintelligent or of questionable mental capacity. One of many different forms and variations of the phrase (for example, "a few sandwiches shy of a picnic," "one card shy of a full deck," etc.). Every time Paul tells me about his latest conspiracy theory, I can't help thinking that he's one egg short of an omelet. Tommy's one egg short of an omelet if he thinks he can convince our mother to let him get a tattoo for his birthday. He says he's going to start a business selling bees as pets—I think he may be egg short of an omelet.
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