When something you ment to think in your head comes out loud, creating a rather awkward situation.
Guy 1: I totally brain leaked last night while screwing my girlfriend
Guy 2: Aww man what you say?
Guy 1: Accidently said "Battenburgs are what make my life complete" about 7 minutes in
Guy 2: I'm Surprised you last 7 minutes
When you have just thought of something completely random and off-topic, and decide to write/draw about that completely random topic.
Man 1: "Hey d00d. Look what I just drew."
Man 1: *shows picture of EPYC Randomness.
Man 2: d00d, that is just pure brain leakage man.
Man 1: I know, right?.