To snap on someone, usually following it with extreme violence. Comes from the short video clip on the internet in which it says "Sometimes... the fat kid... just ain't hungry!" and follows with some kids throwing some (presumably) food at a fat kid, and he just walks over and punches one of the kids in the face.
"I hate Duncan, I'm glad he's gone. It's too bad we never got to see anyone go 'fat kid ain't hungry' on him."