"That's it" means you are so annoyed that you are going to do something about. EX. (Parent to child) "That's it! You've been naughty all day long, now I am sending you to your room!" A "rodeo" is a special kind of sport popular in the Southern and Western USA. Other countries also do rodeo, such as Australia and some countries in Latin America. Basically, rodeo involves trying to ride an angry animal. The animal, a bull (male cow) or a horse, is very wild and tries to throw the rider off. People earn points by how long they can stay on the animal. The wild horse ridden in rodeo is often called a "bronco." In your reading, Rory is making fun of Lorelai's cowboy boots. This is because rodeo riders wear these kinds of boots as well. Although cowboy boots and shorts is fashionable for young women these days, to some people the combination is culturally weird. Personally, I like it. Here is the wikipedia entry. I posted the English one because the Korean one is very short. http://en.wikipedia.org/wiki/Rodeo

You could replace "that's it" for "that's enough", "I'm done talking" or "I had enough" Rodeo is a sport, rodeo rules = rode rocks, rodeo is great, i like rodeo, etc