Mauer, lay back. You just had surgery. You're losing your shirt, man.

Mauer，躺下。你刚做完手术。你快要不剩什么了，兄弟。

If you loaned him all of your money or most of your money, you could lose your shirt – that is, you could go broke.

如果你把所有的钱或大部分的钱都借给他，你可能会丢掉衬衫——也就是说， 你可能会破产。