Its New York Slang meaning if you wanna fight lets go
John : Marcus im bitch slap you
Marcus : So what you waitin for nigga shoot the heady
In NY it means to fight someone one on one.
Yo, let's go outside and shoot the heady!
Want to fight someone head up, ingage in a fight one on one
ingage in a fight one on one, if someone is a bitch you call them out and say "I want to shoot a heady" meaning you want to fight them one on one