A dingbat is a term used by scientists to define humans (typically female) who exhibit a permanently affixed lack of common sense. This condition is usually the result from a combination of sluggish thinking, naivety, and poor reasoning skills. It is sometimes a side-effect to emotive reasoning (IE - when presented with a complex task, bursting into tears and sobbing instead of committing themselves to learn).
Dingbats are also notorious for committing blatant logical fallacies, then stubbornly sticking to them despite being proven wrong.
To date, it is undetermined if these individuals are truly hopeless, or if they can eventually be coached out of their own idiocy.