1. When someone knows how to do something right but at that instant he does it wrong even though he is pro at it.
2. When someone is thinking of saying/doing one thing but does the other.
*You are driving on the freeway and you knew you shouldve takin the 110N exit but you took the 110S for some reason*
Your friend: Dude I thought you knew you had to take the 110N
YOU: Ya I did, just had a freakin brainfart.
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