Sometimes when you're talking to someone, and you're just on a roll, you'll combine words. These are called contractions. Some examples would be can't, he's, should've. Well, some genius was saying 'you can't' and turned it into 'yan't.' Yes, genius put a contraction...into ANOTHER contraction.
"Do you think I can eat all of this pudding in less than thirty seconds?"
"Obviously, you're not cool enough. Yan't."