"Right, because the second someone doesn't agree with you, they're having a tantrum."

He doesn't even know what he's saying anymore, if he's honest. He's just angry, the feeling eating him up inside. He almost feels like he's not in control of himself anymore, just spitting out the first words that come to mind without thinking about them, because thinking means coming face to face with the wall of horror that is Tartarus.

And he's spend all day (weeks, months, since he got on the turtle) dealing with that, and the new terror that is its potential repercussions. He can't deal with it right now.

"But no, you're the only one who could possibly have anything important going on, right?" That's not even based on anything she's said, it's his own feelings of helplessness (uselessness) coming through. This is a side of Percy he usually only saves for gods (Hera) and monsters, but the truth is that this has been building for months now, and where else could he possibly release it?

Not that that's going to be much comfort once it's finally out of his system.