Learn Italian: Questo ragazzo è un cattivaccio e io lo odio. - This boy is a mean guy and I hate him.

The suffix -accio is a pejorative, meaning it adds a negative, nasty, or ugly nuance to a word. Since cattivo already means "bad" or "mean," turning it into cattivaccio intensifies it, making him not just bad, but a truly nasty or despicable guy.

Why does the sentence say un cattivaccio instead of just using it as an adjective?

In Italian, you can easily turn an adjective into a noun by simply placing an article in front of it. By saying un cattivaccio, the adjective becomes a noun phrase meaning "a very mean guy" or "a nasty piece of work," rather than just describing the boy.

Italian usually drops subject pronouns. Why is io included before lo odio?

You are right that subject pronouns are usually dropped. Including io here adds strong emotional emphasis. The speaker is actively highlighting their personal, intense reaction to the boy's bad behavior, making it sound more like "and I hate him!"

Just as a refresher, why does the pronoun lo come before the verb odio?

lo is a direct object pronoun representing the boy ("him"). In Italian, these pronouns must be placed immediately before the conjugated verb, whereas in English they usually come after the verb.