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1.
When you go shoulder deep into a womans vagina, its an extreme underground sex technique
guy : hey , lets go all the way tonight
girl : you mean Shoulder Deep?
guy : yeah Right in there, Shoulder Deep
by Bentleh September 23, 2012
 
2.
A state of being where one is immersed extraordinarily deeply into a project or situation.

Originating from farm life, where cattle and horse breeding often requires literally going "shoulder-deep" into an animal to either fertilize its eggs manually or to check for a pregnancy. This is only gross the first dozen times. Ask your veterinarian or local hick for further details.
Man, I have to get my nerd on and start coding this back end content managed system of this web site my damn self. I'll be shoulder-deep in figuring it out.
by CadeRageous July 31, 2008