East Berlin and nightlife is a sweet combination for someone looking for inexpensive beer and chilling. For the rock/metal people East Berlin feels like home.
Lots of nice, somewhat modest -both in size and decoration wise- metal/rock bars in the East Berlin area can be found. I.e. Punk/hc metal based Amnesie (www.amnesie-online.de) with occational live shows, Halford club apparently for more traditional heavy metal and Paules Metal Eck (http://www.paules-metal-eck.de/), which was by far the cosiest metal bar I myself visited during my stay at the Friedrichshain area.
Prices are very decent, pints are full and the local bartenders friendly yet not that keen to discuss with the tourists. Athmosphere is introverted, but at least you get to relax and observe rather than getting into too much interaction with the native drunken metalheads - who are, as far as I know - very serious about their musical orientations, especially the old school people.
If you succeed in getting to talk to the locals they most likely turn out to be very nice and polite under their grumpy, shy masks, but it seems to me they would rather consentrate on staying in their own small group of friends, leaving out occational and more likely accidential glimpses at the weird outsiders intruding their home bar, still remaining polite and friendly if interaction should happen.
As for women, in metal/rock bars there is hardly any trouble with harrassing men as there are none (see description above, lol). Streets are mostly safe, and by night populated with mostly foreign and local students only interested in drinking and partying. If not making any trouble, there is only a very slim chance of getting into one. Some descreteness, especially in areas known to be populated by neonazis, is encouraged, though.
Best thing especially for the Norther Europeans with their excessive drinking habits, is that when ever you swich bars you can purchase a beer, a liquor or wine bottle of your preference from any corner store on the way all night through. Bars close their doors when costumers finally leave or pass out, but as there is access to alcohol any time, the party is never over.
Gotta love you, East Berlin, gotta love you.