Sure Nigee. You're right, those are reasonable questions that show you're "genuinely interested" in learning. I'll answer them for you.
"Why did Hitler pick on Jews in particular, what is it about the Jewish religion that would make people hate them that much (ignore current situation, focus on historical Jewish behaviour)?"
1.) Hitler 'picked on' (a historically accurate word, people get picked on all the time, let's not overstate what Hitler did here, it clearly wasn't that big of a deal) Jews because he was a white supremacist Aryan bastard that deserves nothing more but the worst afterlife scenario ever envisioned by any religion in world history.
2.) Personally, I don't know what it is about the Jewish religion that made Hitler hate it so much. Rumor has it that when he was 5, he was playing on the playground and a Jew accidentally blew air on him, so he hated them from then on.
3.) By "historical Jewish behavio(u)r," I assume you mean things like being uber-rich all the time, so much so that you should hate Jewish people for no other reason. I mean dude, Sheldon Adelson. Fucker. But if that's not enough, Jews historically have giant noses, and it seems like they're so terrible that they can't stop breeding people with curly hair. What the fuck, you know?
To answer your other question:
"I have no idea but is there something peculiar to Judaism that would upset normal non-Jewish people?"
Well, Nigee, there are a few things, actually. First of all, the religion starts with the letter "J" which is the letter of the devil, whose name is Jatan. That's why everyone hates Jainists too. Secondly, and more importantly, there's this rumor that Jewish people feast on Christian baby blood, and that over Pesach, which is one of their holidays during which the worship the devil Jatan, the only thing they're allowed to eat is this weird bread stuff that's soaked in the blood of a pure Christian virgin. Pretty sick stuff.
I hope that entertains all your "genuine" interest on the matter, Nigee.