At my school, right now, currently sitting behind him

Claim that you are a buddhist and that the shirt he is wearing is offensive to your religion.

I'd just act like a total sperg and ask him if he's unironically a Gnatsee, and if he says no, then ask him why he has that cool swastika on his shirt. Tell him you really like it. And then if he tells you it's an anti-Swastika act all sad and disappointed and if he's Jewish or Gay or something.

Call him a faggot

Could be it's the only shirt he can wear with a swastika on it that he can get away with at school. Maybe he's a hipster wearing it ironically.

Smack his stupid edgy backwards cap of his head and say "nice ccamo pants faggot".

That place looks familiar. Is it on a California community college campus?

I don't think anyone that goes to school has the level of anonymity of random public encounters. He would sacrifice his entire intellect in face of sounding like the biggest and weirdest retard of all so I doubt he'd do that.

(heil'd)
You could tell him you used to play that game all the time, but then you started getting into some other games. You know, the one with the tanks and stuff. The combat one.

If he asks you about the holocaust, just tell him you never watched that movie, don't like historical drama.

Just adding to my previous post, you can claim hinduism instead for extra oppression points.