Smalltalk? (ed: perhaps not quite fair, as message passing/oo is arguably smalltalk's sole paradigm. Common lisp CLOS is another that's also rather clear, but also rather explicit.)

Ed2: there's also Dylan, but again rather explicit: https://opendylan.org/documentation/intro-dylan/objects.html

As I understand it, rust is rather low on ceremony:

https://doc.rust-lang.org/book/ch17-01-what-is-oo.html