Jacknifing 

When a man has an orgasm while his penis is semi-erect.

"Man, I was so sexed-up last night - I started jacknifing the second she put her lips on my cock".

Jacknifing by Wobberino September 28, 2005

Jacknifing 

When a hammock is set up taller than it is wide.

Wow, that person is jacknifing in their hammock like no one's business.

I mean, I've seen people jacknifing at a 90 degree angle before, but that person is jacknifing at an impressive 20 degrees.

Jacknifing by katgumball May 23, 2016

Jacknifing 

when you bend a dog in half and stick your knob in its mouth while someone else does it in the poopchute with a strap on. This way you and the other person can rub rusty sherrifs badges.

I jacknifed my collie last night. I think he might of liked it.

Jacknifing by dangerous dave April 13, 2005