The act of achieving orgasm and/or genital secretion via ones thought process with no physical aide whatsoever.
"I had this raging hard on last night and all I could think about was Tyler Perry dressed up as Madea. Unfortunately I was too drunk to masturbate before I fell asleep. Shortly thereafter I was fairly certain I woke up pissing my pants. Once I came to, thankfully, I had realized I was only brainjacking." - Michael Richards

Albert: (sees Mikey making a face) Is he taking a dump?
Mollie: No, he's thinking real hard! - Look Who's Talking (1989)
by Mr. Douchébag November 27, 2009
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What Super Mario does in Super Mario Odyssey (as seen as the mario fish in the gif)

Check it here and in the gif

Etymology:
Hitler first mentioned this word which may be what he did to Hinderberg in order to get in control of Germany.
Ed: Wow man, Mario can brainjack stuff in this vid look dude in the gif

Fred: Cool, did you know Hitler also did that?
by TheTroll73_[Ezman] June 17, 2017
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To deliberately use someone else's brain to solve a problem or answer a question, rather than your own, even though, with time and effort, you could solve the problem yourself.
I could've worked out the answer to Fermat's Last Theorem, but I brainjacked Brian instead.

Rather than look at the map on the wall to find her way, she brainjacked me.
by Novosapien October 19, 2009
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when you have a repeating song or phrase that has taken control of your brain
i've been brainjacked by soldier boy
by nicholas barker March 5, 2008
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