English really does have a number of idioms based on slandering other cultures/ethnicities. For the Low Countries, there's "going Dutch" and "Dutch treat" (= "splitting the cost", presumably as a dig at perceived stinginess), as well as "Dutch courage" (=false courage because you're drunk), and then there's the "Dutch wife"; meanwhile, the French in the English imagination are supposed to be lascivious, giving rise to terms like "French postcard" (=porn), "French letter" (=condom), "French measles" (=syphilis), and "French kisses". "Welsh rabbit" is a bread-and-cheese dish, mocking Wales for being poor, and all this isn't even mentioning the words and phrases that are actual slurs against Jews, the Roma, African-Americans, and Native Americans.