Math Teacher: "Divide eighteen sugar cubes into three cups of coffee so that each cup has an odd number of sugar cubes in it."
Wise Guy: "That's easy: one, one, and sixteen."
M.T.: "But sixteen isn't odd!"
W.G.: "xxxxxx, xxxxxxx xx xx xxx xxxxxx xx xxxxx xx xxx xx x xxx xx xxxxxx !"

Fill in the correct letters to make the last sentence a punchline.