One word describing making an uncharacteristically stupid mistake? [duplicate]

I am looking for one word to describe making a mistake that ordinarily should have been well within your ability to perform properly.

For example, if someone is considered especially gifted in perceptual organization, yet they fail to notice how to open an extremely simple lock, what type of mistake is that?

The connotation I'm looking for is something like a gross blunder, or an uncharacteristically stupid mistake.

The one word can be any type of word, i.e. noun, adjective, verb, etc. For example:

• "You have made a (noun)."
• "You just (verb)ed."
• "That was very (adjective)."

Words like "gaffe", "blunder", "mistake", to me at least, don't indicate the extreme uncharacteristicness of the stupidity involved.

How about lapse (sometimes referred to as mental lapse)?

From Oxford Dictionaries:

lapse: a temporary failure of concentration, memory, or judgment

As per the OP's question, a lapse is one word that describes "making a mistake [on a task] that ordinarily should have been well within [one's] ability to perform properly ... an uncharacteristically stupid mistake"

Brain fart would be a good two-word answer.

From Oxford Dictionaries:

brain fart: a temporary mental lapse or failure to reason correctly

It's two words, but consider using:

Senior moment - an instance of momentary forgetfulness or confusion that is attributed to the aging process

Although senior is part it, this can apply to anyone who fails to do something they usually could.