Anyone living in Korea knows that Koreans pronounce wi-fi like "Wi-pi", so the shirt would say
"WHY PIE?"
and underneath there would be a picture of a pie with the wi-fi symbol cut out on the top
Example:
http://i42.tinypic.com/mm3ix1.png
(forgive the quality, it was made in ms paint using free use clipart, so it's quite rough)