It was always called the "fanny" at our house. And I still call it that today. I'm from a Polish family and the word "dupa" was used only in slang talk.
My father always called it tuchus which he mispronounced by making the first vowel a long O sound. I think that he liked to talk to me about things like getting shots in my tuchus. Still today I start to get hard when I hear the word.
In our house it was the yiddish word tuches too. The closest to English pronunciation is "took-us", and it means buttocks in yiddish. When I hear it now it brings back some feelings of embarrassment, but not excitement. In terms of RT's and suppositories, even when we were very young my folks would not have said "we need to put this in your tuches", they would have used the word rectum. You might get spanked on your tuches, but you had your temperature taken in your rectum. I have read that "tuches" might be the word that the word "tush" was derived from.
When we were very young we were told to call our butt a hiney poop was called grump and my dick was a tinker.
I usually used the word " Butt ". My Dad used either the word: " Bee--hind " or " Bottom " when my childhood misbehavior reached critical mass and my (bare) BeeHind or (bare) Bottom was nearing or about to get a "tanning".
As a romanian kid, I liked the usual term here - fund - who literally mean "butt" in english and also its diminutive - funduletz (funduleț) who literally mean "little (cute) butt" in english.Most often used by my mom was some terms derived from the german "popo" like "popou", "poponetz", "poponel"
Arse, Bottom, poop shoot. I liked poop shoot the most. She takes it up her poop shoot.I love that it sounds so dirty, makes me want it.
Poop shoot is a good one, my sisters used it. My wife and her high school harlots referred to it as the “Hershey Highway”.
It would depend on the context of course. Rump, tuchas, butt, rear end, fanny, behind, ass. When formally, rectum or rectally, which is not exactly the same as butt.
Sonny years back I stumbled upon a video with a couple of girls, probably around 10, giggling and referring to it as the … ba-donk-a-donkWhich, besides being kinda cute the way they giggled while saying it, was definitely one of the funnier terms for a rear end I’d heard!
It was always referred to as “bottom” in our family. My mother used it the most. That word is still my favorite. So simple and common a word, yet it remains so loaded and powerful for me. I think of it as polite, informal and not crude. I think since my exposure to it early on was almost always when it was used when my mother or a nurse was speaking to me, it makes me feel submissive whenever someone says it to me to this day. (Unless they are referring to their own bottom of course)