I am looking for a word/phrase that means "being temporarily stupid/silly" and fits in these situations.
Situation A Some guy solves a math problem using a very complex method, and some other person shows him a very simple solution. The guys then says: "Oh! Right! I just ___(requested word/phrase)."
Situation B Someone is calling a friend using his/her cellphone, and suddenly yells "Where's my phone? I can't find my phone!" And we can say this person is ___(requested word/phrase)
Situation C Husband gets ripped off but doesn't know about it, and wife shouts: "What were you thinking? Did you ___(requested word/phrase)? How could you fall for that crap?"
Situation D Someone wants to say something but immediately forgets, and he/she mocks himself/herself: "Oh I just ___(requested word/phrase)"
To those who know about Chinese, I am looking for a translation of 脑袋短路. I've asked this on our Chinese site, but the answers there had some controversies. One option is "blank out", which works for D but not the other three. Other options include "brain glitch", "brain fart". But google search tells me these refer to mental illnesses rather than just being temporarily stupid.
Thanks for all the answers that are already here! It seems that there are more ways to express this than I have thought. So if you have a new idea please feel free to add an answer or comment even though I've already accepted one. Due to the possibility that a single word may not work for all the four situations, a specific answer to only one of them is also welcome.
Best Answer
"Blank out", "brain glitch", and "brain fart" are not mental illnesses. They are all legitimate, albeit possibly crude, vernacular for temporary stupidity.
There are others such as "senior moment". This is a facetious reference to the kind of absent-minded dementia occurring in the elderly.
Interestingly enough, Google translates 脑袋短路 as "short circuit". You can use the same metaphor in English:
and so on.