* Adjective: When used to describe something or someone as being mentally deranged or extremely foolish, it functions as an adjective.
* Example: "That's an insane idea!"
* Interjection: When used to express strong emotion, like surprise or disbelief, it acts as an interjection.
* Example: "Insane! How did you do that?"
The specific part of speech depends on how it's used in a sentence.