Second, rotten fruit will probably make you sick if you do try to eat it. And rotten language can make people sick, too. In other words, it not only fails to give positive nourishment, it can cause negative harm. Words can wound a person very deeply. Words can be like the virus that transmits the disease of meanness or vulgarity from parent to child or roommate to roommate or colleague to colleague.
Rotten language makes people sick if they are forced to eat it.
Third, rotten fruit smells bad and makes the atmosphere unpleasant. I recall a couple of men in graduate school in Germany who seemed to carry the aroma of vulgarity about them. All they ever seemed to laugh at was sexual innuendo. The pitiful thing about it was that the nearer they got to the gutter the more they laughed. With their mouths they created an atmosphere like a stinking locker room.