I told the kids in one class a fraction-related joke today.
A guy walks into a restaurant and orders a pizza. The waiter asks if the man would like the pizza cut into 4 pieces or 8 pieces. The man replies, "Better make it 4. I could never eat 8 pieces!"
There were a few pained grimaces of non-understanding, and a general lack of comprehension. When we started talking about it, how the guy would be eating the WHOLE pizza, no matter whether it was cut into 4 pieces or 8, a few kids started to get it.
One kid had his hand raised the whole time, and when I finally called on him, he asked, "How old is that joke?"
I said, "I'm not sure, but pretty old."
He then said, "Oh, no wonder it's not funny."