eat sb's lunch字面意思是“吃了某人的午饭”，实际上是表达“打败某人”（to be much more successful than someone）。

例句：

Unless we're careful, foreign competitors will eat our lunch.

如果我们不小心谨慎，外国的对手会打败我们。

I've been practicing really hard because I refuse to let my nemesis eat my lunch again.

我一直在努力训练，因为我不想让对手再打败我一次。