Envy of your unborn descendants who will live in the future and have access to awesome future technology.
Person 1: Someday they'll invent chips you can have in your head that can access the internet.
Person 2: Oh man I want one.
Person 1: It won't be for a hundred years though.
Person 2: Aww, man! So those lousy future people will get to do it but not me? Lame!
Person 1: You have a case of grandchildren envy!
The guilt trip parents lay on their single childless adult children after they've been cooing over other people's babies. otherwise known as the "why haven't you given me grandchildren yet" disease
"My parents developed grandchild envy when I turned 22. They'realways asking why I haven't given them any grandchildren yet."