That's a paddlin'
Wikisimpsons - The Simpsons Wiki
After becoming a teacher at Springfield Elementary School after the teachers went on strike, Jasper was teaching Lisa's class. He threatened kids with a "paddlin'" if they did anything wrong, including simple stuff like looking out of the window.
Behind the Laughter
"That's a paddlin'" has became a minor meme on the Internet and is famous for Jasper threatening simple things with a "paddlin'". It has became somewhat of Jasper's unofficial catchphrase.