If Danny moved to Gotham, I think he would feel a little threatened. So he decides to try and scare the other gothamites first, to like show he's not weak or whatever.
It's his first day Gotham university. Everyone is introducing themselves with casually saying some absolutely insane facts about themselves (like how they beat the shit out of a goon the other day. Like how insane is that? I mean sure, anyone in amity wins fights with normal ghosts on the regular, but those are ghosts. They don't change, and once you know them it's easy. Humans tho? Much trickier, especially keeping them alive).
It's his turn now. He has a plan, but he needs something tough and hard to do it. He reaches inside his pocket, but he doesn't find any rocks or anything. Instead there's batarang. Guess that'll have to do.
Danny waves at everyone nervously "hello, my name's Danny Fenton and..." He takes out the batarang and takes a bite out of it "...I eat stuff" he says, with mouth full of metal.
The whole class stares at him in bewilderment. The sounds of metal scraping and chewing sounding too loud in the silent classroom.
--
Danny eats rocks. And stuff.
People assume him eating batarang is like... A sign of a rising villain, bc.... That's foreshadowing as hell, you can't lie to me.