Learn Farsi: این فکر بد نیست.

Demonstrative words like این (this) and آن (that) are exceptions to the usual noun-adjective rules. They always come directly before the noun, and they never use an ezafe to connect to it. So you simply say این فکر (this idea).

The Farsi word for 'bad' is pronounced just like the English word. Is that a coincidence?

It is actually a true cognate! English and Farsi both belong to the Indo-European language family. Because they share ancient roots, بد sounds exactly like the English word "bad" and means the exact same thing.

Why do we use نیست for 'is not' instead of adding a negative prefix to است?

The verb "to be" is a bit irregular. While you normally make a Farsi verb negative by adding the prefix نـ (na- or ne-), the word for "is" (است) changes completely to become نیست (is not). Just like all other verbs, it is placed at the very end of the sentence.

Since this lesson is on compound verbs, does بد نیست count as one?

Not exactly! A true compound verb combines a noun or adjective with a "helper" action verb (like "to do" or "to give") to create a brand new action. In this sentence, بد is just a regular adjective describing the idea, and نیست is the simple verb "is not". However, getting used to seeing an adjective parked right next to the verb like this is great practice for the structure of real compound verbs!