Gonna buy this book (Berlin 1945, The Downfall)

"Probably the most amusing story is how the Red Army occupied a huge
underground command center south of Berlin. A caretaker was taking
Soviet troops on a tour when a phone rang. One of the soldiers picked
up the phone to hear a voice barking at him in German. The soldier
shot back in Russian: "Ivan is here. Go to hell." -- and hung up."

Here's one excerpt:

Air raids were so frequent, with the British by night and the Americans by day, that Berliners felt that they spent more time in cellars and air-raid shelters than in their own beds. The lack of sleep contributed to the strange mixture of suppressed hysteria and fatalism. Far fewer people seemed to worry about being denounced to the Gestapo for defeatism, as the rash of jokes indicated. The ubiquitous initials LSR for Luftschutzraum, or air-raid shelter, were said to stand for ‘Lernt schnell Russisch’: 'Learn Russian quickly'. Most Berliners had entirely dropped the ‘Heil Hitler!’ greeting. When Lothar Loewe, a Hitler Youth who had been away from the city, used it on entering a shop, everyone turned and stared at him. It was the last time he uttered the words when not on duty. Loewe found that the most common greeting had become ‘Bleib übrig!’ — 'Survive!'