She's not used to it. She grew up where the sibling closest to her in age was ten years older, and she grew up with Axel, who we know is a tool.

Axel: I am not.

Rhi: when I was 13 you pushed me out of my little sniper nest, and I broke my arm. 

Axel: because you shot me in the ass with BB gun.

Rhi: I did that after, and to be fair, you got lucky you turned around. I missed my mark. All because of some stupid ass girl.

It's okay, Char, Rhi will enjoy watching you piss off Axel. I know I will. *whispers* is okay 

Rhi: is he not? Super creep alert!

Sergio: *takes rocket launcher* I show you something funny. *shoots rocket directly in front of Chester and watches him fly back* 

Understandable.

Billie: *smiles a bit and nods* so long as Clary isn't around I will. *looks at it* wanna try it out?

It's a psychotic sort of adorable.