It is a phrase used by people usually in high school, it is another way for saying "what a joke" or "you're yanking my chain"
Example 1:
Susan: "Me and Jayden had sex and I think I'm pregnant"
Yasmin: "What a yank susie you fucking slut"
Example 2:
Teacher: "We have a surprise test this period"
Students: "WHAT A FUCKING YANK"
Susan: "Me and Jayden had sex and I think I'm pregnant"
Yasmin: "What a yank susie you fucking slut"
Example 2:
Teacher: "We have a surprise test this period"
Students: "WHAT A FUCKING YANK"
by goonsquadfruitylexia May 27, 2015