cowboy
verb. To kill a person with an excessive amount of bullets, this is usually done by associates of a crime syndicate who wish to send a message to those who would cross them.  The action itself is done by pointing a gun (preferrably automatic) at the victim, and squeezing the the trigger while moving ones hand up and down, left and right, spraying bullets into the victim like it's 1929.
Did you hear what happened to Dutch Schultz when he angered Banana-Nose Maldonado? Maldonado had the Teacher and some of his boys cowboy him.