Also, while the efficiency part is correct, I would disagree that we "don't have humour." It's just that Germans have only two types of humor, and both can be misleading:
1. There's the type of humor that is extremely sarcastic and wicked, and that more innocuous people barely recognize as funny.
2. And then there's the type of droll humor that emerges after the consumption of seven to nine pints of beer and that more sober people find simply obnoxious.
That's it -- there's not much in between, I'm afraid. And changing a light bulb... well, that's serious handyman business and definitely nothing to joke about. So wipe that stupid grin off your face.