- Dutch uncle
Dutch uncle is a term for a person who issues frank, harsh, and severe comments and criticism to educate, encourage, or admonish someone. Thus, a "Dutch uncle" is a person who is rather the reverse of what is normally thought of as avuncular or uncle-like (which would be indulgent and permissive).
In Britain, at the time of the Anglo-Dutch Wars in the 17th century, England and the Netherlands were at each other’s throats. At this time the English language gained a whole array of new insults (including "Dutch uncle"), such as:
These colorful (though now incongruous) phrases became part of English usage worldwide, and some are still in use.
One other 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 behaviour is defined in the book Culture Shock! Netherlands: A Survival Guide To Customs and Etiquette as "practical, direct, outspoken, stubborn, well-organised, blunt and thinking they are always right." According to that particular source, these are the alleged reasons behind the English term "Dutch uncle." Another book that advocates this theory is The UnDutchables, which assigns comparable characteristics to Dutch people: "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." 
Still another possible origin may be the marriage of the Dutch William of Orange, who later became incumbent of the British throne, to the English Mary II, in the late 17th century. When the English and Dutch navy were combined during this period the English sailors viewed the Dutch with some resentment, and unwanted advice or orders from Dutch sailors purportedly were said to be from "my Dutch uncle."
- Bolt, Rodney. The Xenophobe's Guide to the Dutch. ISBN 190282525X
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