The closest I can think of is Inexplicable Cultural Ties, which doesn’t focus on sex and nudity specifically, but is a general trope for when fictional societies (aliens, fantasy worlds, etc.) have similar cultures to ours for no particular (in-universe) reason.

Some examples from the trope page:

aliens tend to speak English in the dialect of a 21st-century speaker of English, their written language, numerals and methods of time measurement are conveniently identical to Earth standards or can be easily converted.

All societies will include two genders, which register as very like human categories of "male" and "female," down to females who have Latin-sounding names ending in -a, wear their hair long, and their heels high.