A shit nack occurs when someone puckers up their stank hole and just toops toops toops scedoops on your face until you have a brown dot on your nose that you can use as target practice.
Poeople who have strong faces. they sometimes drink warm cans of Bush on their front porch, and do impressions of a retarted kid with horrible breath. ususally this person will have a crumb on their eyelid that they refuse to chew, and they always have a daughter, and they make sure you know it.
Jesus Christ, let's get the fuck outta here. Shitneck Tom's coming around the corner.