Half-jack 

You get so uninterested in masturbating, that you stop before you cum.

Peter: Dude! I was so baked last night, I was whacking off and got bored and stopped.

Paul: Just a half-jack then?

Half-jack by Goldfish408 March 4, 2010

Half-jack 

The process of exciting male genitalia until it is partially erect in order to help the refractory period after getting the first "easy" orgasm out of the way.

Joe half-jacked so that later when he has sex with Jennifer Whoreton he would be able to reduce the time between sexual excursions.

Half-jack by LanguidLover July 19, 2011

half jack 

Jacking off and ending right before you’re about to cum and then proceeding to workout right after to maximize T-levels. Proven way to get your biceps bigger
Better Pre-workout than Gnar Pump

Me: Hey Joe, why couldn’t you sumo deadlift 450 today?
Joe: Bro, honestly, I didn’t half jack today, I’m just not feeling as good
Me:Pussy

half jack by Half-Jacking December 12, 2018

half jack 

"Half Jack" refers to a person who is gender confused, and possibly considering sex change surgery. A person who either feels that they are of the wrong gender, or that they are half male and half female.

Mary was really into Tom at the party last night, but she wasnt aware that he's "Half Jack" and had no interest in her.

half jack by Scott the Heirophant February 9, 2008

Half a cup of Jack Daniels

How to know when you're serious about your drinking.

Measure your booze by cups not ounces.

Half a cup of Jack Daniels:

For this recipe you need Half a cup of Jack Daniel's.

If you don't have Jack Daniels you can substitute three quarters of a cup of Jim Beam.

Half a cup of Jack Daniels by Cowboy682 March 19, 2026

Jack and a half 

To express that something will require an above-and-beyond effort. Originates from software developers using the royal cards (Jack, Queen, King and Ace) from a standard deck to play Planning Poker.

It's going to be a jack and a half to gather all that test data.

Jack and a half by JettaC January 18, 2011

half jacked-off

a synonym for half-assed, half baked, et al. Usually used to render scorn on a famous person/celebrity who, for all their glitter, charisma and talent really puts forth a miserable effort in said situation.

Ben Affleck's cinematic efforts of late have been generally of the half jacked-off variety.

half jacked-off by Virgin Suicides June 16, 2017