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1.
The art of hiding an erection while sitting and leaning one's upper torso at a 45 degree angle betwixt one's chest and lap. The owner of said erection then proceeds to arch their back in such a way that makes them appear to be sitting upright. This causes said erection to recede into the body causing a "turtle shell" effect.
"Dude, my Spanish teacher is so hot...she had me turtle shelling all class."
by JoPaGeRi.TBC August 15, 2007
 
2.
In Call of Duty: MW2, when someone puts a Riot Shield on their back and goes prone so they can not be knifed.
Ah, i'm playing knife only and this guy keeps Turtle Shelling me.
by Mr.Wizenhymer September 08, 2010
 
3.
What happens when you hold your poop for too long. When you finally sit down on the toilet, you let loose only to realize that it may have been on the verge of popping out, and that you probably had less time to wait than you thought.
John: "Bro, Sidney was over for 6 hours last night and I had to shit so bad!"

Steve: "Damn, son. Did you drop a deuce with her at your place?"

John: "No, but I was turtle shelling it like a mothafucka. Almost shat everywhere."
by 2toedsloth December 16, 2011
 
4.
The art of hiding an erection while sitting and leaning one's upper torso at a 45 degree angle betwixt one's chest and lap. The owner of said erection then proceeds to arch their back in such a way that makes them appear to be sitting upright. This causes said erection to recede into the body causing a "turtle shell" effect.
"Dude, my Spanish teacher is so hot...she had me turtle shelling all class."
by JoPaGeRi.TBC September 02, 2007
 
5.
V. The act of taking someones backback when they're not looking, taking everything out of the main pocket, turning the bag inside out, placing everything back in, zipping it up so as the zippers are on the inside making it difficult to open back up, and placing it back next to the person before they find out what you've been doing.
Dude 1: Dude Joe's not looking, grab his bag.

Dude 2: I got it.

Dude 1: Give it here.

Dude 2: What are you doing with it?

Dude 1: Im turtle shelling it.

Dude 2: Nice, go go go.
by Dickfacelardass101 March 09, 2009