It isn't a phrase which is in common usage today. Essentially it means petty criminals.

These are terms from around the 18th century though Pirates is a word that is still used today and there are modern day pirates and cyber-pirates. Dandy- I think this was usually used to describe a person, usually a male, who liked to dress up in very stylish and colorful clothing for the time period, the 1700's. They may also have appeared somewhat feminine. Think of what people call today as a metrosexual. Aristocrat- Aristocrats were mostly the wealthy and ruling parties of the 1700's. They had money and political power. I notice you are from Russia and think of the ruling class in Russia pre-World War I. Like the Romanovs, or some of the people who ruled under them that had power but not as much as them. People also tend to view them as thinking they are better than people who aren't wealthy and just working class people. Having an aristocratic attitude is referring to this kind of thought. Pirate- In the traditional sense of course is the guys who sailed ships on the ocean and attacked other ships and stole theri money. In today's world you can have cyber pirates who who download music, games and movies illegally. They are also called pirates. You can still find ways to use all of these words in modern day talk but mostly just to have some fun and it can lead to interesting conversations on their own :)