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1. Past tense of crack up.
2. cracked up to be. Reputed to be. This expression is always used in a negative way, as in I don't think this book is all it's cracked up to be. It relies on the now obsolete use of to crack up to mean "to praise extravagantly." It appeared in The Kentuckian: "He is not the thing he is cracked up for" (May 28, 1829). [Early 1800s]
3. Under the influence of crack (a form of cocaine). For example, "Who's cracked up, who's cracked out, and who's dead?" ( World News Tonight, ABC-TV, May 12, 1992). [1980s]