When you are cleaning a window:
"You missed a spot." or "You can come do mine."
At work, when someone gives me the exact amount of the purchase:
"Keep the change."
As previously discussed in its own thread, when asking how many sugars someone takes:
"None, I'm sweet enough."
When you tell someone you go to University:
"I went to the University of Life."
Some counter quotes to these would be appreciated.