You're a real nitwit. Why should you badmouth his girlfriend in his face?

你真是个糊涂虫，怎么能当他的面讲他女朋友的坏话那？

16.饭量小 eat like a bird

She eats like a bird. A small piece of bread will be enough for her.

她的饭量特别小，吃一小块面包就够了。