How would I describe vanity as a verb. He is being ________.

vain

Also you can use http://www.thesaurus.com and look that word up to see alternatives.

I looked up vain and it said that it means worthless. I don't understand how that is related to vanity.

Writeacher is correct.

Check these definitions.

http://dictionary.reference.com/browse/vain

Thanks Writeacher and Ms. Sue :)

To describe vanity as a verb, you can use the phrase "being vain". So in the sentence "He is being ________," you would say "He is being vain."

To arrive at this answer, you can follow these steps:
1. Understand the meaning of the word "vanity". Vanity refers to excessive pride or admiration of one's own appearance or achievements.
2. Recognize that "vanity" can be used as a noun or a verb.
3. Identify the verb form of "vanity" by converting it into a verb phrase. In this case, "vanity" becomes "to be vain".
4. Apply the verb phrase to the sentence, resulting in the phrase "He is being vain."