v. tr.

1. Referring to automobile accidents, when a car is totalled to the point of folding in on itself, much like a jacknife.
Holy shit, Zach's new car got jackknifed by a pickup truck! What a tard!
by SabDek April 19, 2003
From what I know, it's when an 18-wheeler is carrying one of those loads, any loads, as long as it's carry a load, and it's going at quite a highspeed, suddenly braking, causing the actual truck itself to brake whilst the load's momentum behind the truck forces itself in motion against the truck, causing the load on the back to be intersecting at a perpendicular angle with the truck. Look at this---> |_ The | is the actual truck and the _ is it's load. The truck (|) is going forward, whilst the load (_) is scraping it's tires horizontally.

A jackknife is also responsible for causing many highway accidents, because when a truck jackknifes, it takes up all the lanes on the highways, and leaves no mercy for the vehicles in its path! Always speed up if you see a jackknife coming toward you if you cannot rapidly get off the highway.
*people driving*
Oh crap dude, that truck is in the process of a jackknife, that piece of shit volkswagon is in our way, guess the only choice we have is to speed up, step on it.
*person in volkswagon*
*ahhhh this is the life, *fart*, beer and hot sauce...boomheadshot.*
by Cobain will have justice. November 27, 2005
When her pussy is so tight, he jackknifed his dick when attempting to penetrate. His dick bends instead of entering.
Girl, you're so wet, yet so tight I jackknifed!


Have you ever seen a dick jackknife?!
by Freyjawired November 23, 2016
1. n.-a pocket knife

2. n., v.-person or object that is bent unusually at a 90 degree angle resembling the shapre of an open pocket knife, as in the case of a car accident or physical movements used in disciplines such as diving, gymnastics, yoga, wrestling, etc.

"That diver has incredible technique! Note how he jackknifes his body to move into that maneuver in mid-air."

"Oh, shit! Did you see that car accident? It looked like that tractor-trailer was totally jackknifed!"
by Lapa November 30, 2005
sex move in which woman on her side bottom leg straight top leg bent up to her chest
i slammed her Jackknife style!
by JBut November 25, 2007
A "Jackknife" is made by dropping a shot of Jack Daniels into a glass of Corona, depth charge style.

Similar to a Jägerbomb.
Bar Guy 1: Just give me a beer
Bartender: And for your friend?
Bar Guy 2: Ill have a Jackknife, cause I'm a real man.
by Muhammed Ali Ganoo September 2, 2008
When a male attmepts to fellate himself however the extreme angles involved cause him to throw his back out, and he is stuck in that position until help can arrive.
Hey, Steve got caught in a Toledo Jackknife, again.
by Benevir August 19, 2007