Teacher! Puck you!

I was teaching one of my youngest classes, a group of 12 five year-olds, when one of the students unintentionally used his middle finger to count. Immediately, all the other kids seized the moment and pointed out to me (tattling is pretty popular with the younger kids) that Kevin had used his middle finger. Rather than make an issue of what seemed to be an accident, I feigned ignorance and pretended not to know what the raising of one's middle finger actually means. So the students collectively set out to teach me, and started yelling, "Teacher! Kevin 'puck you!'" And they repeated it over and over (with gestures) until I gave some sign that I understood. I have to admit- I was pretty entertained by all these little kids yelling this out, especially with a "P", but frankly I'm baffled- where do they learn this stuff??