YOU SAID:
i cant believe youd do that
INTO JAPANESE
あなたがそんなことをするなんて信じられない
BACK INTO ENGLISH
I can't believe you would do that.
INTO JAPANESE
あなたがそんなことをするなんて信じられません。
BACK INTO ENGLISH
I can't believe you would do that.
That didn't even make that much sense in English.