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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. DouchΓ©bag November 27, 2009
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