>>11332800>Booty, badonkadonk, and dumptruck are definitely all up there in terms of size I feel, in fact it's probably in that order.Makes sense.
>it'd probably be ass, before that, butt, and then continuing on, it would be rump, rear, tush.I can see what you mean. Though I would say ass/butt are somewhat interchangeable, if only because they are the most commonplace of any words for rear end, and definitely have a mixed level of tameness and lewdness between them. On one hand, some people find ass to be vulgar, though on the other, it does seem to depend on the context of its use like you said. Likewise, butt is tamer, but can have a certain lewdness to it when spoken in a particular context.
When it gets to rump, rear, and tush, those do seem be fairly equal, if only because they're probably the most innocuous terms, along with things tuchus or bum.
I guess really any of those (even ass in certain cases) can be used to describe a girl who just has a normal looking backside, even if it's not particularly shapely or notable.
Obviously, it gets tricky when talking about truly pathetic looking asses, like ones that could rival Hank Hill's, though those do seem to be rare, at least in my opinion. I'm more forgiving towards smaller rears, so long as they have some shape to them and aren't concave or really off looking (that one anime with the muscular chick who had an ass that looked like someone dented the sides is one such example), even if the girl is fairly flat but has a nice rear, I can appreciate that (Fuu from Samurai Champloo is one such example).