Back Stack 

A sexual position where two females lay on each other back to back. One famale is on all fours while the other lays back to back on top of her. The male can finger one and use his dick on one, rotate using his dick, eat both out, or eat one and finger one.

Guy: Dude i hung with these smokin hot chicks last night and eventually convinced them to let me get em in a back stack.

Guy's friend: Nice dude! Lemme know next time and maybe we can tag team.

Back Stack by ARandomWhiteGuy May 7, 2009

back sack attack 

The assault of one's testicles from behind. Generally, the victim is bent over, however a standing attack up the legs is also commonplace.

Often times, the assailant will yell "back sack attack!" either at contact, or after the strike is complete.

Winding up for a kick, Ben positioned himself behind a bent-over Matt. Using mostly the flick of his foot unto the scrotum, Ben yelled "Back sack attack!" before Matt ever got the chance to react. Devolving into his fetal position, Matt sat writhing in pain.

back sack attack by MrPistachio February 9, 2013

Back-sack 

Back Sack is the backside of ones scrotum.

A: Yo dog, I can't believe you just ball-tapped me from behind, you got all back-sack.
B: Ew, check out that old guy's back-sack hanging out of his pants.
C: Check out Katz's shaved back-sack.
D: Mom, Jacob put his back-sack on my face.

Back-sack by J'Nathan Bo'Jingles May 25, 2008

Turtle-back Sack 

When a males scrotum is hard like a turtle's shell.

Man, these tighty whities gave me a turtle-back sack.

Turtle-back Sack by Ank D. Holla January 8, 2009

Back Sack'n'Crack 

Three words defining the hair removal procedures involved in hair salons of a male from the areas of the carpet back, ballsack and butt crack.

Usually coupled with a hairless jock area.

'You're a fucking hairy cunt'
'No way dude, I'm off on a jolly this weekend at a health spa. As part of the package I'm getting the 'ole back sack'n'crack'
'I hear that'

Back Sack'n'Crack by Krikpoh Kneebracket January 28, 2007

Back-stacking 

Inserting a full bottle of hard-A into your anus to get drunker, quicker.

"I caught my lady back-stacking a fifth of Beefeater."

Back-stacking by Ace Monroe May 31, 2017

back sack 

the back of your peaches

the back of your nut sack gets hit and your like ahh my back sack.

back sack by S.A.R.S. July 2, 2008