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1.
A hot sexy cowboy who sexes up Ennis on Brokeback Mountain.
"That fishing pole ain't never touched water. Jack Twist?! Jack Nasty!!!"
by Ted'n'Jeff March 05, 2006
 
2.
Refers to a scene in the 1997 short story and 2005 film Brokeback Mountain where the character of Alma confronts her husband, Ennis about his ongoing relationship with the character Jack Twist.

Denotes a fan of the story and/or movie.
Quote:"Don't lie to me Ennis. I know what it means. Jack Twist? Jack Nasty."
by Marceline8 March 13, 2006
 
3.
When your female sex partner refuses to have sex and you masturbate until she gives in.
I had to do the jack nasty last night to get laid
by mk6turbo June 02, 2014
 
4.
Similar to asstastic, used in reference to a particularly outlandish body part.

Something really incredible and/or truly astounding.
Dude, last night we were at the strip club and the stripper had a jacknasty set of twin towers.
by Diggerdowntrigger August 25, 2006
 
5.
Any article of clothing used to wipe up ejaculate after masturbation, usually stored under the bed or in another discrete location.
Check it out! These boxers are as stiff as a board, they must be Jimmy's jack nasties!
by Kash65 May 07, 2012
 
6.
Alright kids, a jack nasty is where a boy usually high school or younger who can't get laid masturbates 'jacks off' into some tissues. Since he is often not one to properly discpose of them, they drift about the room and eventually make their residence beneath his bed.

The resulting hard, crusty tissue wad peeking out from beneath the mattress... Is a jack nasty.
Person A: What's with the tissues, dude?

Person B: Nothing!

Person A: Man you was makin' jack nasties!

OR:

Man that chick was so fine but I'll never get with her. I cry alone at night and make jack nasties.
by Alexander C.R August 09, 2005