That snake in the grass reported me to the boss.　

KEY & NOTES:

那个口蜜腹剑的家伙到老板那里告了我一状。

没错吧，＂藏在草丛中的蛇＂就是那种＂伪装成朋友的很阴险的人＂
（someone who pretends to be your friend while secretly doing
things to harm you ）！这样的人，往往容易被忽略，却是最可怕的，
所以我们一定要慧眼识人！把敌人当朋友，那可是件很伤心很痛苦的事情．
It's upsetting to learn that someone you once viewed as a good
colleague is in fact a snake in the grass.^_^