身體：坐下去的那一塊
這一組就是字面義本身，其他所有用法都從這裡出發。
noun · B2
The part of your body that you sit on. It can also mean the opening at the end of the bowel. It is a rude word, so most speakers keep it for close friends, or for moments when they are annoyed.
屁股
核心畫面
You can think of arse as the plain, rude name for the part of the body you sit on — the lowest and least part of a person. Nearly everything else the word does can be seen growing out of that one picture. It is the part that stays on the chair when someone will not get up. It is the part you name when you want to shrink a whole person down to something worthless. And it is what you reach for when you want to say that something is as bad as it gets.
「arse」可以想成一個很直接、也很粗的字：人坐下去的那一塊。它是身體上最不體面、也最沒有面子的部位。英文很多用法都…更多收起
「arse」可以想成一個很直接、也很粗的字：人坐下去的那一塊。它是身體上最不體面、也最沒有面子的部位。英文很多用法都像是從這個畫面長出來的。懶得動的時候，屁股就是黏在椅子上的那個東西。看不起一個人的時候，就用這個部位把他整個人縮小。要說某樣東西爛透了，也拿它來當比較的底線。所以你會看到同一個字，一下子是身體，一下子是罵人，一下子只是脫口而出的一聲。From the word’s history
Wiktionary traces arse through Middle English ars/ers and Old English ærs to Proto-Germanic *arsaz and the Proto-Indo-European root *h₁órsos, meaning 'backside, buttocks'. German Arsch and Dutch aars come from the same root. So the body-part picture is not a later development — it is where the word starts.
依照 Wiktionary 的說明，arse 從中古英語 ars／ers、古英語 ærs 一路上溯到原始日耳曼語 *arsaz，最遠到印歐語根 *h₁órsos，意思就是「後面、屁股」。德文的 Arsch、荷蘭文的 aars 同源。也就是說，身體部位這個畫面不是後來才加上去的，它本來就是這個字的起點。
Wiktionary entry 'arse' (packet source_ref kaikki:3f6f69a190036ae4:502950985)
Four branches
用屁股代表一整個人
英文常拿身體最不體面的部位來指人。把一個人縮成他的屁股，可以是罵他，也可以只是很不客氣地說「你」。
noun · B2
A person you think is stupid, unkind, or too pleased with themselves. It is a rude, insulting word. People also use it about themselves, after they have done something silly.
混蛋／討厭鬼
屁股當成「爛透了」的代名詞
既然這是身體最不體面的部位，它就很方便拿來當「最低分」用：東西爛、話很鬼扯、事情出錯，都可以往這裡丟。
noun · C1
Said straight after repeating what someone has just claimed, to show that you do not believe it at all. It is rude, and it usually sounds angry or scornful.
才怪！／鬼扯！
屁股黏在椅子上：懶跟催
人在偷懶的時候，最明顯的就是屁股沒離開椅子。英文抓住這個畫面，發展出一整組講懶惰、講催促的說法。
noun · B2
Used to tell someone to stop sitting around doing nothing and start doing something. It is rude, so it sounds impatient, or like rough joking between friends.
別再坐著了，動起來