Phrase invented by east coast rappers Mobb Deep to signify someone who acts hardcore until they actually have to deal with the reality of "the life of diamonds and guns". A coward who is shaken up by the harshness of innner city life.
"He ain't a crook, son. He just a shook one." - Mobb Deep
To be "shook to the core," you simply can not fathom something resulting you to be in a state in which you can not easily speak other words than "shook to the core." This is a verb used to properly demonstrate your feelings towards something or someone's actions or state of being.
Gabriel: "Did you see what he just did?"
Human: "Yeah, I am surprised!"
Gabriel: "I am Shook to the core! I can't believe it!"
Human: *nods in confirmation*