Yes is one of the many notable quotes featured in YTPs. Yes is a way of telling characters to agree with another so they don't annoy the shit out of each other. Yes is often also used to show someone is happy about something.
Yes is symbolized by the color green and a thumbs up for some reason. There are also a bunch of dumb words that mean the same thing, like yeah, yep, ya, uh-huh, certainly and Grammar Nazis love them.