hey-oh
Robin: Oh, please. I'm so sick of the meat market scene. Guys are like the subway.
You miss one, and another comes along in five minutes
Lily: Unless it's the end of night, and then you get on anything.
Robin: Hey-oh. (Having a high five with Lily)

What does 'hey-oh' mean? Why the two girls have the high five?
Does Robin said 'hey-oh' and had the high five to express her happiness that they share the same idea on guys and train issue?

Question

hey-oh
Robin: Oh, please. I'm so sick of the meat market scene. Guys are like the subway.
You miss one, and another comes along in five minutes 
Lily: Unless it's the end of night, and then you get on anything.
Robin: Hey-oh. (Having a high five with Lily)

What does 'hey-oh' mean? Why the two girls have the high five?
Does Robin said 'hey-oh' and had the high five to express her happiness that they share the same idea on guys and train issue?

Answer

You are right, they are saying "hey-oh" to express to each other their excitement for that idea.

"hey-oh" doesn't really mean anything.  You could say anything there, "Oh yea", "all right", "Awesome"

Hope that helps!