http://wiki.answers.com/Q/What_is_the_meaning_of_the_saying_%27stupid_is_stupid_does%27

А сабж, имхо, сказан Форрестом Гампом.

Умный тот, кто поступает по-умному.

"Many of you have seen the movie
Forrest Gump, in which Tom Hanks
utters the famous words, “Stupid is
as stupid does.” Mrs. Gump was very
clever and protective of her son, and
she taught him these words to prepare
him for those unfortunate but inevitable
times in his life when he would be called
“stupid” because of his below average
intelligence. Yet, as we quickly discover
in the movie, even though Forrest’s IQ
is low, the life he lives is far richer and
more successful than most could ever
hope for."