A total lack of recognition.
A silly mistake.
Can be stress related.
"I had a total brain-fart when she asked for my number."
An unwarranted interjection in an otherwise controlled environment.
Teacher: So you see, we now have only three weeks before the biology exams.
Student: That means I will only have three more driving lessons before my driving test.
Student: Sorry sir, just a bain-fart.