The word is used repeatedly in the novel "The Moon is a Harsh Mistress" by sci-fi master Robert A. Heinlein
A yammerhead is:
1. The obnoxious guy sitting in the next table over at the restaurant, calling the waitress every five minutes because his drink is too warm, he does not have enough sauce, and the steak is a tad undercooked.
2. An idiot who objects to agreeing a proposal by unanimous consent because he wants to hear "debate," which is "essential in a democracy."
3. There is at least one in every room. If you cannot find him/her, then you are it.
Used to describe a person, usually a nagging wife, that constantly babbles and complains about even the smallest of issues. This person will usually express their resentment or displeasure in a public place such as a grocery store or restaurant.
Yammering Netty literally means Clamorous Toilet; from the
verb Yammer: To utter or say in a complaining or clamorous tone; and the noun Netty: The British slang word for public or outside toilet. - See also: Chatter Box
Herold took Alice out to a nice restaurant and all she did was babble about how he never takes her anywhere nice. Alice is such a Yammering Netty.