'does it not sound natural?' Yes, you can call someone that. Normally, though, 'perfectionist' doesn't have a negative meaning, so the two adjectives are a little strange together. Some people think 'perfectionist' is insulting, and it can be if you want it to be. However, "Pretty Little Liars" is a popular show that uses the same awkward combination of negative and positive adjectives in the title, so it's not wrong.