YOU SAID:
He cannot be the nicest person ever seen on Earth.
INTO JAPANESE
彼は地球上で見た中で最も素敵な人にはなれません。
BACK INTO ENGLISH
He can't be the nicest person I've seen on earth.
INTO JAPANESE
彼は私が地球上で見た中で最も素敵な人にはなれない。
BACK INTO ENGLISH
He can't be the nicest person I've seen on earth.
You've done this before, haven't you.