First things first: dah- MEH
Indispensable in conversation, can't be found in Japanese textbooks; the word means "bad", "prohibited"... and a whole bunch of other things.
It seems everything in Japan is "dame". Talking loudly is dame. Pointing your feet at someone on the train is dame. Yawning in public is dame. Using cell phone on the train is dame. Laughing too loudly is dame. Pointing is dame. Sticking chopsticks upright (in a bowl of rice or something) is dame. Blowing your nose in public (god forgive you if you did it in a restuarant!!!) is dame. Accidentally foregoing a "desu" or "masu" (polite add-ons) is dame...
I am very quickly finding out that there are a lot of unsaid "rules" here... and breaking them is very painful. And by painful I mean, I get chastised. "Tami-san, dame desu yo. DAME DAME DAME!!" Followed by a fast and furious explanation of sorts (which is usually not understandable), with a final summary flourish of "dame yo".
I cannot imagine Americans living by so many rules.