Short legs and elbows

Three classes today, so I don't have so much free time to fill, but let me tell you about a few interactions I've had with students recently.

Firstly, there's a girl in one of my 2nd year classes who was talking to the teacher who sits next to me in the staffroom a couple of weeks ago. She clearly wanted to interact with me and was fascinated by my blueish eyes, and complimented me on my height. She said I had "long legs" and pointed to herself in comparison but I think she couldn't find the word she was looking for. I came out with "tansoku" - a word meaning "short legs" which is how the Japanese describe their own most common body type. The girl thought it was hilarious that I knew this word (most of the new 2nd years don't know I speak a fair amount of Japanese), and now she mentions it whenever she sees me around the school. I saw today her as I was going into the classroom beside her's, and she came over and pointed at herself excitedly and said, "Tansoku tansoku tansoku tansoku tansoku!". I just nodded in agreement.

In another 2nd year class, there's one slightly rowdy boy who for the last two classes has tried to persuade me to say "pizza" ten times. Or rather, he asked me to say "piza", which is the most common Japanese pronunciation. I refused, fearing I was being tricked into calling myself an idiot or something, but he would inevitably say it himself before pointing at his elbow and asking, "What's this?". After the first class where this happened, I decided to do some research on the internet. I found my way to 2-channel, a popular Japanese message board, and discovered that the pizza thing seemed to be a rather innocent game where you trick the other person into confusing their knee and elbow. In Japanese, "knee" is "hiza" and "elbow" is "niji". After saying "piza" ten times, when the person points at their elbow, your mind is supposed to be tricked into saying "hiza" instead of "niji".

Anyway, the second class where it happened I refused to do it again, because...well...I'm like that. But this time, every time the boy, who sits at the front, would get to the, "What's this?" stage, another boy further towards the back would shout out, "Elbow" (this is all in English, by the way). At one point, the boy at the front tried to trick me into doing it by writing "piza" ten times in his textbook and asking me to read it. Again it failed, again he did it instead - but this time he said it really quietly, and added, "What's this?" in a whisper. Out of nowhere, the boy towards the back, who had been engaging in the communication activity that the students were supposed to be doing at that point, shouted out, "Elbow". It was like a reflect. I burst out laughing.

Anyway, I had a similar experience today as I came back from a class on the same floor as the "piza" boys class. He was hanging around the stairwell (the other boy wasn't in sight at this point) and tried to get me to do it AGAIN as I went past. Exactly the same process played out, and when he said, "What's this?", again out of nowhere, the other boy popped into the corridor and piped in, "Elbow!".

How can I leave this madness behind?