Clubbing in Berlin is steeped in a sense of culture and history that doesn't really exist anywhere else in the world. It can all essentially be traced back to the fall of the Berlin wall - all of a sudden two groups of people were united, and one of the big melting pots for East and West Berliners were the raves occupying abandoned and derelict buildings buildings in the East part of Berlin. These were egalitarian spaces, where people were encouraged be express themselves in whatever way they wanted.
The clubs that define Berlin's nightlife today are direct descendants of these parties (to varying extents). The obvious examples are Berghain and Tresor, both Berlin institutions that have existed in some form since the early days of the 90s. These clubs embody the same kind of individualistic, expressive ideals. Berghain is especially famous for its hedonism - once your inside, pretty much anything goes. Sex, nudity and drugs, everywhere. Because of this, some of the clubs are very selective of who they let in. Dressing up nicely will guarantee that you'll be turned away. It's not about being glamorous or having money (like it is in Vegas for example), it's about having a good time and dancing for like 36 hours+.
Obviously not all clubs in Berlin are like this, but the same ideas of individualism and hedonism kind of characterise the entire party scene in the city.