A proper term used improperly in ebonics. Some city White boys think it is cool to use ebonics, and so they proclaim that they were shook.
This form of ebonics is just represents a lack of education, as it is improper English to use the past participle form of a verb when an adjective is necessary (i.e. shaken).
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