on top of the world 字面意思是这个人在世界顶端，但实际是说此人处于最快乐或最成功的境界。类似汉语里的幸福至极，心满意足。

Both Mark and I are feeling on top of the world.

马克和我都感到非常高兴。

I just told him to never forget that the guys who put you on top of the world can put you under, too.

但我要说的是，你永远不要忘了那些将你托起到世界高峰的队友，他们也可以将你打入深渊。