Superlative form of grumpy: most grumpy.(adjective)
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Use "grumpiest" in a sentence
"• And finally, the title grumpiest man of the week goes to author Howard Jacobson, whose view of modern life doesn't appear to have been lifted by his long-awaited Booker triumph with The Finkler Question."
"It reminded my wife of her father, who we dub the grumpiest man alive."
"ConcernedParent says: mccain is trying to win the record for the grumpiest man alive."