Term originated from Jamaican patios. Used to describe people who are always up to mischief and adventure. Recently this term has been adopted by the independent clothing brand GNK which original stood for grizzle neck kids.
Term would be used in the following way: "See my boy Trilla yeah, he's been a grizzle neck from day"
"I know my mans a straight grizzle neck but he ain't ever treated me like your fool of a boyfriend"