another point: maybe sometimes you hear some natives saying, "Bastos mo!" it's actually just a shortened way of saying "Ang bastos mo!" But in formal way of speaking of writing it, you must include, "Ang" before the adjective.

Well, apparantly you know what the words "ka" and "mo" mean right?

They are used dependeng on how you start your sentence.

It's a very long explanation but since you are asking about when you are describing someone you are talking to;

1. If you started with the word "Ang" and you are talking directly to a single person, you end it with "mo"

Ex. Ang ganda mo. - <em>You are pretty.</em>

     Ang kulit mo.    - <em>You are stubborn.</em>

     Ang bastos mo. - <em>You are rude.</em>

2. If you started your sentence with an adjective with the prefix "ma" you, you end it with "ka"

Ex. Maganda ka.

     Makulit ka.

     Bastos ka. (there is no need for a prefix for this word and some more others)