Jack in a Box 

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!

Jack in a Box by Quagmire517 September 9, 2011

Jack in a box 

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!

Jack in a box by Robertion August 22, 2011

Jack In A Box 

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.

Jack In A Box by fucklayton September 23, 2015

Jack in a Box 

When you masturbate inside of a box

I wanna Jack in a Box.

Jack in a Box by DirtyRed October 31, 2017

Jack-In-A-Box 

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!

Jack-In-A-Box by MTF January 22, 2009

Jacksonville jack in a box 

You are recieving a rim job when you shart in the rimer's mouth with great force

Hey man, last night i gave her the Jacksonville jack in a box and she loved it.

Jacksonville jack in a box by Spawj May 20, 2014