In our household it is referred to as "rode in on the short bus today"...not very PC but I have just finished reading Amos's honesty thread.

In this state, I have bounced my face off pedestrian crossing signal boxes, mistaken road signs, such as "Xing", for foreign languages, lit pencils and have been known to peer into the fridge several times, before recalling that I was actually looking for a pen.

Fortunately, my family has come to accept my occasional bouts of single minded preoccupation and predisposition to serious brain fade.