RICHARD: You know, when I was ten years old, I knew exactly where I wanted to work.
LORELAI: That’s because you were always picked last for Dodgeball.
Dodgeball is a game where two teams throw balls at each other while trying to avoid being hit themselves. The main objective is to remove the opposing team entirely by either hitting them, catching the balls they throw, or forcing them to move from the court to avoid being hit.
For many years, it was a popular choice for Physical Education classes in the US, but recently has come under scrutiny because of its potential for bullying and injury, and some schools have modified, phased it out, or banned it.
In Dodgeball the smallest, least confident, least agile, and least athletic participants are generally eliminated first, so they are usually the last to be picked for a team. Lorelai is saying her father at ten years old would have been the kind of wimpy nerd who is bullied in Physical Education class.