You were fighting with someone in the camp, Nico being your best friend he had you back in the fight, he was watching and occasionally flipping off the other person to piss them off. You were really angry at the person because ever since you joined the Camp half blood the person treated you like shit, until they said something that set you off

Bully:This is why no one likes you, and why your mom left you

When the person said that Nico was furious, and punched the bully in the face