a temporary (but varyingly frequent) condition of the brain, often incorrectly referred to as a brain fart
(farting implies expulsion, which is the opposite of the occuring situation), in which one is attempting to speak but the thought refuses to move from the bowels of the brain to be expelled by the mouth.
1 - I was attempting to explain what happened to my bff
, but had one of those all-too-common instances of brainstipation.
2 - I was trying to do my presentation in front of the class from memory, but had total brainstipation and clusterfuck