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3.
Used in reference to the rapid-fire single leg motion usually executed by dogs when rubbed in "that right spot".
Sean: Stop making out with my dog, bro. You know her nubbin is at the base of her tail.
Paul: Dude, she came over to be rubbed. What else am I gonna do?
Sean: Bro, that's a scratchgasm. You just went all the way with my dog. Uggh.
by Gloves December 25, 2007
 
1.
A feeling of EXTREME pleasure that occasionally occurs when a male sratches his balls. (generally some of the looser skin from the sack) The pleasure is equal to or greater than the pleasure of an orgasm.

WARNING:
This wonderful wave of pleasure usually results in a frantic scratching of the testicular region that leaves men red, chapped, and chafed. Stop scatching immediately after the scratchgasm for your own safety!
It's ok to scratch your nuts at work or school. You're a man, people expect it of you. But if you have a scratchgasm, try not to moan. That usually freaks people out.
by Joo ZipperDick July 10, 2008
 
2.
That feeling you get with a really good backscratch.
She scratched my back and it felt like I was going to have a scratchgasm.
by Bill Fey May 30, 2008
 
4.
The feeling a man gets when he first wakes up in the morning and scratches his ball sac.
I knew today today was going to be a great one right after I had my scratchgasm.
by The Turd Nazi November 17, 2010