This a typical expression of excitement and generally precedes Ya-Ya Yearse in the form of a chant.
Person 1: Hey, are girls with big boobs going to be at the party tonight?
Person 2: Yes. There will be big boobs everywhere.
Person 1 and 2 Chanting: Yimmie Ya-Ya Yimmie Ya-Ya Yearse! Yimmie Ya-Ya Yimmie Ya-Ya Yearse!