So I'm new to Oblivion, and I swear to Sithis, nearly every NPC in the game hates me after I initially talk to them. They're like "enough talk", etc.. I like to manually raise their Disposition afterwards, but it gets tedious when somehow everyone hates me after the first time I say hi to them.

Are people in Cyrodiil just rude to Argonians or something? Is it a stat thing? What is up with this?

It's because Argonians start with a Personality of 30, which is just north of "turnip" in terms of raising NPC disposition.

Yea this!

Don't worry, the more quest you do, the more people like you. I believe buying things from merchants also increases their disposition for you, making it easier to barter with them.

The majority of characters I play are Orcs, so everyone just glares at him when they first talk to him. Make sure not to talk to them with your weapons drawn, that lowers their deposition, just play the game as you normally will and soon the NPCs will like you.

A little neat thing, your character will react differently to different NPCs if you go into Third person. The NPC might like you and have a huge smile, but your character will glare at them.

Yes, Fame is the quickest way to improve Disposition, up to a certain point. You can raise the disposition of just about everybody by up to 20 points just by being a famous hero. Of course, Infamy works in the opposite direction, so if you're an evil Argonian, you're not going to be making many friends.

High Personality helps a lot. You get 1 point of Disposition for every 4 points of Personality.

Having your weapon drawn (or your fists raised) when talking to people lowers their disposition by 10 points.

And then there's bribery and the speechcraft mini-game.

Those are the significant ways to affect disposition. Race and Faction have smaller effects, typically a point or two in one direction or the other.