Here's a breakdown:
* Moldy hay: Hay that has been stored improperly and has developed mold. This gives it a dirty, grayish-green color, a musty smell, and a rough, dry texture.
* Comparison: By comparing someone's hair to moldy hay, the speaker is emphasizing that the hair is:
* Unkempt and dirty: The moldy hay suggests the hair hasn't been washed or cared for properly.
* Unhealthy and dull: The color and texture of moldy hay imply that the hair is dry, brittle, and lifeless.
* Unpleasant to look at: The image of moldy hay evokes a sense of disgust and repulsiveness.
Overall, the phrase "his hair like moldy hay" is a harsh and exaggerated way of describing someone's hair, likely meant to be humorous or sarcastic.