Top Definition
In the act of masturbating to online pornography, when your hand reaches the top of your shaft and slams the desk and creates a thunder-like sound.
person 1: Is it storming outside? I hear thunder but I don't see any lightning.

person 2: Oh that's just John in the next room over thunder fapping. He must be watching some good stuff.
by Spilner April 15, 2011
When your entire body cramps up from a single masturbation session with the most glorious orgasm you've ever had.
Damn dude, I saw some shit so crazy last night I thunderfapped and spent the morning in the ICU
by Marcus Kraulter November 19, 2011
The art of fapping with rediculous might or strength.
I was totally engrossed in my thunderfap session when my mom walked into the embarassing!
by SallieKatt April 12, 2011
The act of fapping very loud and quickly, much like thunder.
Is that a storm, or is my roommate just thunder fapping?
by pimpassnigga September 11, 2012
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