水面上那層綠
字面的一支，也是整個詞的來源畫面。
noun · B2
The green, slimy layer of tiny plants that grows on the surface of still water, such as a pond that nobody looks after.
（池塘）綠藻浮渣
核心畫面
One way to hold this phrase: a pond nobody takes care of, sitting still through a hot month, with a green film spreading across the top. Nothing there is moving. Whatever floats up ends on that surface and stays. The picture is harmless in itself — it is only tiny plants — but it looks and feels unpleasant, and it sits at the bottom of the list of things anyone would want. Both uses live inside that single image; one points at the water, the other points at a person.
pond scum 的畫面可以想成：一個沒人整理的池塘，在最熱的那個月靜靜地擺著，水面上慢慢鋪開一層綠膜。裡面什麼都…更多收起
pond scum 的畫面可以想成：一個沒人整理的池塘，在最熱的那個月靜靜地擺著，水面上慢慢鋪開一層綠膜。裡面什麼都不動，浮上來的東西就停在那層上面。這個畫面本身無害——說穿了只是些小植物——但看起來、摸起來都讓人不舒服，而且它排在所有人想要的東西的最後面。兩個用法都住在這張圖裡：一個指著水，一個指著人。Two branches
拿浮渣來罵人
把「最底層、沒人想碰」這個感覺整包搬到人身上。這是比喻，不是另一條來源。
noun · C1
A very rude name for a person you think is worthless and cannot be trusted — as low as the green slime that sits on a still pond.
人渣；爛人