dumb dip

A momentary lapse of intelligence. Even the smartest people are hovering above "the dumb" most of the time, and when intelligence lapses, they "dip into the dumb" - hopefully not for very long, before they recover and pull out of the dumb.

Not to be confused with a memory lapse, as dumb dips involve people with their mental faculties fully in tact.

"Did you see that guy on Jeopardy last night? He was doing so amazing but made the dumbest mistake on Final Jeopardy and lost everything. That was a very costly dumb dip!"