Let's talk about the bluntest knives in the drawer of the animated world.
Dee Dee from "Dexter's Lab"
As for how dumb she is, I'll take one scene. Dexter has built a brick wall just behind the entrance of his lab. Dee dee opens the secret door and runs into the wall, then gets up and runs into the wall again, before recovering herself and running into the wall again, before getting up again and running into the wall again.
Ed from "Ed, Edd N Eddy"
Ed may be so brainless that Eddy can stick his arm in one of Ed's ears and make it re-appear out the other. But he does have many uses. Such as a shovel or a pnumatic hammer. Or in the episode "a Glass of warm Ed" as a food storage facility.
Then from the hitseries
Avatar, the last Airbender there's
Ty Lee
This girl is a highly skilled acrobat who walks on her hands just as easily as walking normally and who's able to take out opponents by pressing accupuncture points at their body. Her physique has the boys wrapped around her finger and they do whatever she askes them to do. But she's also as smart as your regular goldfish in a bowl, she has no concept of the evil ways that her "friend' princess Azula is dragging her into. Deep down she's slowly becoming aware that she sitting at the wrong side of the fence and that people are getting hurt because of her actions. But as long as she remembers how to smile and being bubbly (And how to inhale and exhale) she keeps enjoying the merits of not being able to comprehend life and taking resposibilities for her actions.
Bruticus from
The Transformers is the combined form of the Combaticons, a decepticon team. Each Combaticon is a militairy specialist in their own right but because they hate each other so much, Bruticus doesn't have their genius, in fact, the only thing that all five Combaticons attribute to Bruticus' knowledge are the things they agree on which is virtually nothing at all. As a result, Bruticus is the kind of Transformer who has to be told what he should do because he can't make a decision on his own. So unless somebody gives him an order, he'd be standing still all day. But when somebody DOES give him an order Bruticus turns into the ideal soldier, who just does what he's asked to do and doesn't ask questions. But that can range to him having to destroy a city or to have him arrange the flowers of Megatron's back garden, just say that he has to do it and he'll do it. Megatron once said of his dumb subordinate that he was one of his favorites and that he wishes he had a whole army of Bruticuses, luckily for all of us he doesn't.
