stupid is as stupid does

Etymology
Apparently modeled on. Attested since at least 1862, but popularized (perhaps independently) by the 1994 film .

Proverb

 * 1) Stupid behaviour indicates stupidity.
 * 2) * 1882 Anthony Trollope: Orley Farm
 * As long as a man can pay twenty shillings in the pound and a trifle over,  what does it matter if all the judges in the land was to call him stupid?'  said  Snengkeld. "Stupid is as stupid does." said Kantwise."Stupid be d--."  said  Moulder."Mr. Moulder, there's ladies  present." said Mrs. Smiley,