Cole is the Black Irish in this film.
Cole McKay is the only member in his family that has the dark hair and eyes. Based on some popular concepts of what "Black Irish" means, it can only be concluded that in this story, it refers to the character of Cole.
Also, in the climactic scene of the movie where Cole and his brother, Terry, are in a stand-off holding guns in the restaurant, Terry utters a line (which is partially garbled and run-together) in which he says the following to Cole:
[Terry to Cole]: "...Black Irish...(garbled)...black licorice, soft, sweet, hollow inside..."
This is Terry referring to his brother Cole's nature as the "Black Irish" in the family. Cole is the Black Irish. Cole is the soft, sweet one (remember the pet rabbit). Cole is hollow inside. That's up to us to decide.
If anyone knows what the garbled words are in that piece of dialoge, I would sure like to know. Please write a new subject and indicate in the subject "Clarified Dialogue" or something like that.
Thanks,
Rob