Slightly related to these "insult another nationality terms", I've always loved the different euphemisms languages have come up with for syphilis. This is probably because syphilis was a disease brought by enemy armies (note: I don't think any of these terms are commonly used today)
English: French disease
French: English disease
Russian: Polish disease
Polish: German sickness
Arabic: Christian disease
Portuguese: Castillian sickness
...Of course, this thread's in the Chinese section of italki, so it behooves me to (try) translate the above for Chinese readers...
我们在讨论英语俗语"go Dutch”的辞源（本义是“做荷兰式”，意思是“AA制）。其实，go Dutch的含义不太礼貌，表示荷兰人很小气。辞源反映历史上英国和荷兰的战争和矛盾。
Just to add to my last comment, and in response to Stephen's, these are my thoughts on the usage of "Dutch" expressions in the UK:
"go Dutch" - neutral expression still said by a lot of people
"my old Dutch" - mostly Cockney, and dying out in modern English. Friendly tone.
"Dutch courage" - the false courage you get from drinking a lot of alcohol. Neutral tone and not a street expression. Probably known and used mainly by older, more educated people.
"Dutch uncle" - the male friend of your parents, who you refer to as "uncle", as a sign of respect. Becoming old fashioned. Neutral tone.
Despite the origins, when people use these terms nowadays, there is no sense of bigotry towards the Dutch, and the origins would be mysterious to the majority of people, in my opinion. I've never heard of any Dutch people having a problem with these expressions, but of course, their usage may not be widely known by Dutch people.
In China, only when a bunch of friends go out for dinner will we split the bill.
In most cases, when girls eat out with boys, the boys will pay the bill, so we needn’t argue with them who pay the bill. If they insist it, we just let them treat us this time. Next time, we can treat him. If there’re only girls or boys, we are not concerned about face-saving thing. It’s easily to say let’s split the bill and calculate how much each one should pay.
I think the old generation for my parents will insist paying for everything. In order to avoid the argument some people will pay the bill silently in the middle of their meal. Also Chinese will invite their friends to have a dinner with their first salary.
This is sort of treat culture in China.
"go Dutch" is used in the UK too. But I've never heard "Dutch treat". I haven't researched it recently, but from what I know, phrases with the word "Dutch" in them hark back to historical trade and commercial competition between Britain and Holland. (e.g. Dutch uncle, my old Dutch, Dutch courage)
In fact, the Dutch can say that they were the last nation to occupy any part of Great Britain. They occupied the Isle of Sheppey (in the Thames estuary) once for a few days when trade relations between London and Holland were particularly bad. I think it was some time in the 1800s but I am sure the mighty Wikipedia can tell us exactly!