四面楚歌不及你一掌致命
[sì miàn chŭ gē bù jí nĭ yī zhăng zhì mìng]
A literal translation would be 'trapped on all sides with no retreat isn't as deadly as your one strike'. It refers to a situation so threatening from all sides yet the user suggests something about you (or the receiver) being more significantly harmful/heartbreaking/destructive.