waacka decka
Pretty much synonymous with "whatever" (aspect of "yeah right")... often used in response to "halt mein"...
Person 1: I said that team was going to win.
Person 2: Waacka decka, no you didn't.
Person 3: Yes I did!
Person 2: Waacka decka, no you didn't.
Person 3: Yes I did!