Dutch uncle refers to a person who issues frank, harsh, or severe comments and criticism to educate, encourage, or admonish (the reverse of what is normally thought of as avuncular or uncle-like, i.e. indulgent and permissive). During the Anglo-Dutch Wars in the 17th century, the English language gained an array of similar insults, such as: ‘Dutch courage’ (alcohol-induced bravery), ‘Double Dutch’ (incomprehensible, nonsense), ‘Dutch cap’ (contraceptive diaphragm), ‘Dutch wife’ (sex doll), ‘Dutch widow’ (prostitute), ‘Dutch comfort’ (saying that ‘Things could be worse!’), ‘Dutch metal’ or ‘Dutch gold’ (cheap alloy resembling gold), ‘Dutch treat’ (social date where the invitee pays for himself/herself), ‘Dutch concert’ (noise and uproar, as from a drunken crowd), and ‘Dutch-bottomed’ (empty).
Another proposed explanation is that the term, often expressed as ‘talk to one like a Dutch uncle,’ originated in the early 19th century as an allusion to the sternness and sobriety attributed to the Dutch. Dutch behavior is defined in the book ‘Culture Shock! Netherlands: A Survival Guide To Customs and Etiquette’ as ‘practical, direct, outspoken, stubborn, well-organized, blunt and thinking they are always right.’ Another book that advocates this theory is ‘The UnDutchables,’ which assigns comparable characteristics: ‘not lacking in self-esteem … caught up in a cycle of endless envy … always speak their mind … frank, obstinate, blunt,’ basically summed up by the phrase ‘the natives thrive on shaking their fingers at and scolding each other.’
The Daily Omnivore 