a black sheep 害群之马
be old dog at something.就是对...有经验; 对...很内行的意思.
goose egg【俚】零分
like a drowned rat 浑身湿透（象落汤鸡）
like water off a duck's back 毫不在乎,毫无作用（如果你对侮辱、指责之类的不在乎可以用,如：Terry said he was too sensitive about criticism and he wanted to be like one of those people for whom it’s like water off a duck’s back）
to teach a fish how to swim 班门弄斧
a litte bird told me that 我听说的；有人私下告诉我的（一般不愿说出来源时所用）
a white elephant无用的累赘东西；沉重的负担
donkey's years 很长的时间
monkey uncle吃惊
rain dogs and cats倾盆大雨
a snake in the grass 潜伏的敌人,口蜜腹剑的人
monkey business胡闹,骗人的把戏；欺骗；恶作剧