"Hello!" said a smiling boy next to me on the train. "Well, hello," I said, startled that anyone should actually use this phrase unaccompanied by at least a giggle and at most rolling on the floor laughing.
Because in Japan the funniest thing in the world to a Japanese student is saying hello to a foreigner. The "hello" joke is to foreigners what the "Why did the chicken cross the road?" joke is to Japanese. They just don't get it.
Why is "hello" such a funny word to Japanese? Until recently, students have been taught English as a foreign language in schools, but have never been comfortable using it. Daring to say hello to a foreigner makes non-English-speaking Japanese nervous (thus the laugh) and such communication is largely something left to the class clown.