Shizuo gets mad easily and he does his outbursts a lot. So I really can't tell if he really hates Izaya, if he is just annoyed by him, or because he just can't hold his temper.

Well I don't think so as mentioned Shizu-chan does tend to get angry easily and a lot of emotion comes out of him in that so it's hard to assume what he's feeling about Izaya-kun but based on that fact I don't think he hates Izaya at all.

It's hard to know what he's thinking, but I don't think Shizuo really hates Izaya.

It's so freaking obvious that he hates him. I hate him too. Izaya is the most overrated character in the series. (Please don't kill me.)

^ HOW DARE YOU BE SO MEAN TO IZA-CHAN TTATT

-shrugs-
He says he does~

EDIT
@pumpkinqueen:
He doesnt get ticked off by everyone though :\

what a simple question

EmoSasuSaku: No, I believe he just says Izaya annoys him and he doesn't know why he fights with him. Remember, Shizuo gets ticked at everyone with his anger.

I guess I am kind of borderline but most of the time, I feel like he wants to murder Izaya.

I went with unsure. He claims he does but . . . we've all seen what Shizuo can do. If he really hated him, why is he still breathing?

Well yeah (Izaya did a LOT of awful things to Shizuo so Shizu-chan probably hates him a lot), but that still can't stop the Shizaya fans from twisting it up in their own way *evil smirk* and i'm secretly hoping their relationship changes (if it magically can) in the future chapters of the light novel :(

Shizuo has hated Izaya from the moment they met, and the feeling is mutual. I understand that some Shizaya fans might want to think otherwise, but I think the best part about that pairing is the boundaries they would have to overcome. Really, though, I think it started out as dislike, and the two just became so convinced that they hated each other that now they really do. However, I don't think either of them will ever kill the other: mainly because of the twins (and Akane, probably). Also, I just don't think Vorona and Celty would ever let Shizuo cross that line, and, as much as Izaya denies Shizuo's humanity, Izaya himself doesn't have it in him to take a life with his own two hands. If they survive lung cancer and head trauma long enough, we'll probably still see Shizuo chasing Izaya around Ikebukuro as old men, waving a walker around (or maybe just waving Walker around) and yelling, "Get off my lawn!" while Izaya acts like Mr. Burns.