Самая примечательная особенность в человеке.
The most characteristic, distinguishing feature of a person
the most notable feature in a person
The most remarkable point of person.
feature IN a person
Uly, as horrible as it sounds, I've actually seen OF a person, especially in overseas publications and website.
Для интересующихся: https://books.google.com/ngrams/graph?content=feature+of+a+person%2C+feature+in+a+person&year_start=1800&year_end=2008&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cfeature%20of%20a%20person%3B%2Cc0%3B.t1%3B%2Cfeature%20in%20a%20person%3B%2Cc0#t1%3B%2Cfeature%20of%20a%20person%3B%2Cc1%3B.t1%3B%2Cfeature%20in%20a%20person%3B%2Cc0 Вот Yourdictinary.com "The definition of characteristic is a distinguishing feature of a person or thing." https://www.yourdictionary.com/characteristic https://forum.wordreference.com/threads/distinguishing-feature-of-in-a-person.3657838/