In a crusty manner; with a crust or in a grumpy, irritable way (informal).
From crusty (adjective meaning 'having a crust' or 'grumpy') plus the adverbial suffix -ly meaning 'in the manner of.' It transforms the adjective into an adverb.
Old sailors earned the nickname 'crusty' because the salt from ocean spray would form actual crusts on their beards and weathered skin—so to speak crustily meant you had the hard, salty demeanor of someone who'd spent decades at sea.
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