It's an adjective. It means something badass, something you shouldn't have done, describes tough situations. Its another word for sooky. It's also used to replace foul language.
Jon: Look at my new Mustang
Eric: Awwwwwwwww shucky now
Tammy: I banged Megan's boyfriend last night cuz I don't like her
Sara: Awwwwww shucky shucky