In Bahasa it means many such as : -It doesn't make sense/Impossible -It is strange -It is just kidding -It is bullshit :D Hope it will help :)

you must be kidding.

Ada-ada aja! this phrase is used for exclamation stating that words fail one. It also can be used when you want to say "What a nonsense!", "are you pulling my leg?" Please follow this link to know how to use that phrase in some contexts reference http://books.google.com.au/books?id=hVo2ZDYbL6gC&printsec=frontcover&dq=A+Comprehensive+Indonesian-#v=onepage&q=ada-ada%20saja&f=false

I think this could be translate as don't make a sense. Use the sentence when you want to answer something as a joke or in subtle way (menjawab dengan cara halus) e.g: A:"Kamu hamil ya???!" (are you pregnant?) B:" Ah, kamu ada-ada aja deh. gak lah..." (Ah, you don't make a sense. it's impossible..)

Apa artinya " Kamu ada - ada aja! " ? In English it would probably translated as " give me a break!! "