DEE DEE DEE
a person who is capable of using common sense, but doesn't.

or

what you say after somebody does something dumb that could of been avoided if they were paying attention

used by carlos mencia
that teacher is such a dee dee dee that she couldn't work at mcdonald's if she got fired.

or

person-"i can't find my keys"
20 minutes later
person-"o here they are, they were in front of me on the table the whole time"
person's friend-"dee dee dee"