Dutch courage

unusual or artificial courage arising from the influence of alcohol. (Viewed by some as insulting to the Dutch.) It was Dutch courage that made the football fan attack the policeman. It will take a bit of Dutch courage to make an after-dinner speech.

the confidence that you get by drinking alcohol before you do something that you are frightened of doing He had another drink to give him Dutch courage for what he might find at home.

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."

Bravery acquired by drinking alcohol. Political and economic rivals during the 17th century, England and Holland fought a series of wars. English propagandists spread the rumor that Dutch soldiers and sailors developed the necessary nerve to fight only after drinking gin and other alcoholic beverages. The Dutch haven't fared well in the English language. Other unflattering phrases are “Dutch treat (you pay for only yourself), “Dutch uncle” (a stern person, especially one who gave you a lecture you weren't happy about receiving), and “double Dutch” (gibberish).