Here's the breakdown:
* About is a preposition.
* As bad is an adjective phrase, with "as" being a comparative conjunction and "bad" being an adjective.
Together, "about as bad" modifies a verb, adjective, or another adverb, indicating a degree of badness.
For example:
* "The movie was about as bad as I expected." (modifying the adjective "bad")
* "He played about as bad as he could." (modifying the verb "played")
Let me know if you'd like more examples!