When someone is so concerned about toilet seat germs, they cover the seat with half a roll of toilet paper, leaving it to appear like it has been mummified. This is called "toilet mummy".

有的人特别担心马桶座圈的细菌，就用一大堆厕纸厚厚地铺在座圈上，把马桶座圈裹得像个木乃伊。这就叫“马桶木乃伊”。

Example:

I was going to use that toilet, but somebody left it looking like a toilet mummy.

我本来想用那个马桶，但有人把它裹成了“马桶木乃伊”。