She 'played/acted dumb' [=pretended to know or understand less than she really did] so we would assign her the easier tasks.
She thinks television is contributing to the 'dumbing down' of America.
Cutting training programs will 'dumb down' the American workforce.
(..) Stand back. Yah! - That work. - Well, what would you do if you're so smart. I'll tell you. But you're too dumb to understand. - What! - Of course your tiny brain is confuse. Guess I'll just have to dumb it down to your level. Sorry I don't speak moron (..)2015 Inside Out
(..) - Loneliness. - Hm. I think there is something in there. I'm going to turn it on for a minute and burn out the dumb thoughts. What did I tell ya. You'll be in Headquarters in no time. Hey, will you look at that? - Whoa. What's happening? - Oh no, they turned it on. (..)2015 Inside Out