stupid is as stupid does

English

Etymology

Apparently modeled on handsome is as handsome does. Attested since at least 1862, but popularized (perhaps independently) by the 1994 film Forrest Gump.

Proverb

stupid is as stupid does

1. Stupid behaviour indicates stupidity.
   • 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,