From Longman Dictionary of Contemporary Englishbored/scared/worried stiffbored/scared/worried stiffinformalVERY extremely bored, frightened, or worried As a child, I was scared stiff of going down to the cellar. → stiff
Examples from the Corpus
bored/scared/worried stiff• Cis, who knew about it, was scared stiff.• Poor kid, thought Alice, he's scared stiff.• And I was scared stiff about having lied to Mel about being single when he hired me.• Mabel was by now scared stiff and frozen cold.• We looked at each other, scared stiff, but we followed Mrs Bullivant upstairs.• He was very naturally scared stiff of using up all his remaining petrol and making a bad landing.• He was scared stiff, thought a ghastly mistake had been made. 