Hades hates Danny. All souls go to the underworld (aka the Ghost Zone) eventually and become part of his domain. But not Danny. He straddles the two worlds like Persephone (side note: holy shit halfa!Persephone can you imagine?), eternally just out of Hades’s control.
So Hades takes matters into his own hands. Every now and then, a portal to the Ghost Zone will appear next to Danny and Hades will try to lure/drag him in. It’s gotten to the point where Danny just carries around a broom and hits Hades with it whenever he tries to start shit.
Mr. Lancer’s class is confused the first time Danny brings a broom to class, but they’re absolutely dumbfounded when he hits the god of the underworld with it and says “shoo.”