courage inspired by drunkenness or drinking liquor.
Origin of Dutch courage
First recorded in 1805–15
Dutch courage is foolish courage or misplaced confidence. Because “Dutch” is used to imply that the courage is not genuine, the term is sometimes perceived as insulting to or by the Dutch. See also Dutch.
False courage acquired by drinking liquor, as in He had a quick drink to give him Dutch courage. This idiom alludes to the reputed heavy drinking of the Dutch, and was first referred to in Edmund Waller's Instructions to a Painter (1665): “The Dutch their wine, and all their brandy lose, Disarm'd of that from which their courage grows.”