"STUPID" has now been classified as a dog-whistle term.
It is in line to become banned as one of the new "N" words.
"STUPID" has been replaced by "SMARTLESS".
Well, then, how about one of the following?
moron
blockhead
idiot
silly
unintelligent
simple-minded
slow-witted
brainless (always a favorite)
thick
empty-headed
bacon-brained
imbecile
foolish
mindless
knucklehead (another favorite)
cork-brained
meathead (Archie Bunker)
fool--never a nice thing to say to ANYONE
goofy
mutton-head