Great Moments in English Teaching:

Noticing that Toyo had a bandage on his hand:
Me: "Hey, Toyo, what happened to your hand?"
Toyo: "I have an artificial arm from a traffic accident in college."
Me: "...Oh."
Why I never noticed this, and secondly why he had BANDAGES on a FAKE HAND is beyond me.

Takashi: "My granddaughter, she has mumps. Hahahahahaha."
Me: "Takashi, did anyone ever tell you that you have a tendency to laugh inappropriately?"
Takashi: "HAHAHAHAHA."
This came after weeks of Takashi laughing about his visiting his father's grave, his tennis elbow, natural disasters, etc.

Me: "Did you get along with your parents when you were little?"
Kazue: "My father used to hit me with a kendo sword."