A penis that looks average until it is aroused and then erects to a size well above the norm.
Andrew: Yes, my penis looks only about an inch long when it is soft.

Slampiece: Well I must admit, your Jack in a Box was a nice surprise!
by Quagmire517 September 9, 2011
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A toy. Not to be confused with "Jack in the box", a fast-food restaurant.
Baby Hugo cried whenever he played with his Jack-In-A-Box. Every time Jack popped out it frightened him. Bad Jack!
by MTF January 22, 2009
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When you have an erection that your girlfriend doesn't know about and you whip it out of your pants and show her your hard on, usually with a really pleased expression on your face.
I was lying in bed reading the other day when Rob pulled down the sheets and sprung his jack in a box on me!
by Robertion August 17, 2011
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Fast food resturant popular in the US, and HOLY in California. With such a wide selection of supreme quality food at such affordable prices, Jack in the Box rules all other fast-food franchises worldwide.
I'm hungry and only have a little money. I KNOW! I'll go to Jack in the Box, get full and have a lot of cash left over!

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by Evil Pumpkin December 11, 2003
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When a girls fists herself and then you put your dick in too and she gives you a handy.
I went to a donkey show in Tijuana and the girl really stepped up her game by giving the bachelor a Jack In A Box.
by fucklayton August 16, 2015
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One of the best fast food restraunts out there. An actual clean restraunt other than hardees or mcdonalds. They make quality food.
Im gonna get me a chicken fajita pita from jack in the box.
by Oz April 20, 2005
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While you are 'jack'ing off, someone walks in on you just as you are climaxing and you ejaculate on them.
Sexy man 1:Dude did you see that American Pie?

Guy 2:Oh yea the one where stiffler pulled a jack in the box all over his grandma!!
by SPsexyman555 September 28, 2011
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