When someone has been smoking weed for so long that their stoner haze doesn't wear off when their high wears down anymore. They are just that dumb/slow all the time.
Stoner while not high: Duuuuuude, where did you put the peanut butter???
Roommate 1: Uh, it's in your hand.
Stoner: Ohhhh yeahhhhh, huhuhhuhuhuhuh.
Roommate 2: (shakes head), man, he is smoked stupid. I remember back in the day when he used to be totally normal.
Roommate 1: Yeah. BEFORE college.