Question: I'm looking for something people from rural area would use, especially when they refer to that person's inability to adapt to the country life.

Answer: 
Per [Wikipedia](https://en.wikipedia.org/wiki/City_slicker):

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> City slicker
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> ***City slicker*** is an idiomatic expression for someone **accustomed to a city or urban lifestyle and unsuited to life in the country**. The term was typically **used as a term of derision by rural Americans** who regarded them with amusement. 
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[![Promotional poster for the movie *City Slickers*, depicting three men in business suits mounted on horses sporting Western-style tack. Billy Crystal is riding his horse backwards, which allows us to see the "I ❤️ NY" bumper sticker on its rump.](https://i.stack.imgur.com/XB6Ct.jpg)](https://i.stack.imgur.com/XB6Ct.jpg)
Another long shot, since the best picks are already taken, but '**burger'**, in its original meaning could be used in derogatory sense. This kind of use originated from XIX century Russian literature, so is more likely to be recognized in countries whose history has been influenced by Russia than others.