That Wouldn't Slither Down in Snaith
Saying from York, UK meaning that a certain form of behaviour is unacceptable - implication that it wouldn't be acceptable in the village of Snaith, near York. The behaviour is so unacceptable that, to personify it, never mind walking or running, it would be unable to even slither around Snaith before being challenged.
"That gentleman has just disobeyed traffic laws and displayed a rude gesture, informing me that I am a masturbator. That wouldn't slither down in Snaith!"