When speaking Chinese, tones are of utmost importance.
For example, when we say, "teacher" or "lao shi." With the incorrect tones, we actually address our instructor as "rat."
I've caught a cold, which in Canada would be fine, except that I'm in Taiwan where everyone looks at you as if you are vomiting molten lava whenever you sneeze or cough. The school advised me to consult a doctor who told me that I did not, thankfully, have H1N1.
Some of my Taiwanese friends tried to teach me to say: "I have a cold."(Cold is gan mao.)
I tried: "Wo you gan mao."
Everyone thought that was just hilarious. Apparently because I said that I have ass hair.
That could have been confusing at the doctor's office.
(As an aside, I still refuse to use the squat toilets but I found a very helpful online tutorial that may help in this matter.)