When to Go: Anytime other than Winter, when Christkindlmarkt (German "holiday" markets) and snow blanket the city, giving it a nostalgic third reich-y vibe.
Where to Stay: Berlin, originally designed to inhabit 5 million, is the only city in Europe with a current population (3 million) smaller than pre-WWII (I learned that from a tour guide who moonlights as a stand up comic). That being so, accommodations (hotels, youth hostels or apartments) are cheap, spacious and easy to find.
Language: Many Germans speak English, and those who don't will pretend that they do so as not to embarrass themselves.
Slang: "Yu vant schot?" (or "would you like to take a shot?") means "I'm sorry for my lack of charm, but if you get drunk, you won't notice"
What to Drink: Beer, enough to not be bothered by your (German) date's "mojo" but not enough to forget he doesn't have any.
Transportation: Germans are known for their expedient, timely transportation and the U-bahn is just that. Fines for not having a ticket on the train are relatively low (11 euro), so it might be more cost effective just to game it. Taxis are easy to track down, although many drivers claim they don't speak English. Despite that, if you sternly yell exactly where you want to go, they'll most often respond accordingly (there's something about people who've lived under oppressive authoritarian regimes that makes yelling at them weirdly effective).
Safety: Polizei are too busy monitoring immigrant Turks or busting other Germans for committing hate crimes against immigrant Turks to notice any of your minor infractions. That being said, don't be an idiot.
Currency: Always carry cash. If you go on a date (in German, I think the word is "platonic business dinner") be prepared to foot at least part of the bill, even if he invites you.
Best HIV/AIDS Test: It doesn't matter, you probably won't be having sex.
Sexual Fun Fact: A 2009 international poll surveyed 15,000 well "traveled" women and ranked German men the world's worst lovers (source: OnePoll.com). Fortunately, Berlin is host to plenty of ex-pat artists from all over the world (top ranked were Spaniards, followed by Brazilians, Italians and French).
Where to Eat: The food in Berlin is generally pretty great. If you're a vegetarian, I must recommend Cafe V (Lausitzer Platz 12, Kreuzberg) it's inexpensive (since you're paying half) and awesome.
Dating Tips: Don't show up late, unless you want to get yelled at (which sounds so much scarier in German).
"Useful" Words and Phrases: The word for pubic hair in German is schammhaar, which actual translates to "shame hair" (typically German). Also, the word for vagina is muschie (pronounced "mushy" ... eek). "Ich habe keinen mein wallet" means "I forgot my wallet." If he asks "what's a wallet?" tell him "it's what you used to make Jews into." He'll feel either awkward and/or guilty and most likely pay! Germans are actually fans of dark humor and sarcasm, but some things (really just the holocaust) are still too soon to talk about. On that note...
Biggest Buzz Kill: It's a toss up between Berlin's oldest Jewish cemetery (pictured to the right), where just 20 of 12,000 graves remain, The Jewish Museum in Kreuzberg (because it's curated for an audience who has never met a Jewish person) and the Tiergarten Antique Market (aka Berlin's largest outdoor holocaust museum), where you'll find antique Judaica (from the 1930s) or knock offs posing as such.
Distracting Fact to Take Your Mind off my Holocaust Fixation: The very first bomb dropped by the Allies on Berlin during WWII killed the only elephant in the Berlin Zoo (another sad fun fact, elephants are super sensitive and smart, and the only other mammals, along with whales, to go through menopause).