You笨蛋You傻蛋
[you bèn dàn you shă dàn]
You are stupid and silly (repeated for emphasis). In Chinese '笨蛋' (bèndàn) and '傻蛋' (shǎdàn) both mean fool/idiocy with different nuances. Here this nickname might imply some endearing frustration with the target person's naivety and lack of sense.