Okay, are you serious about this? It means Bruce Banner has some serious emotional baggage combined with a gamma radiation fueled genetic mutation inside him that is always there. It's not just an issue when he's hulked-out, he's always dealing with what's inside of him.
And that's just with what's fully explicit from the screen. Extrapolating gives a whole lot more. Fear and anger are very closely linked emotions, and Banner not only has a lot of anger inside him, but also a lot of fear, both of what's he could do, and what's done to those around him. Also, he's shown to deal with some level of depression, and in many ways depression is anger turned inwards. Bruce hates himself, he's depressed, and afraid, and all that means he's pretty much angry all the time. He hides it, manages it, but he doesn't have to get angry to turn into the Hulk, he's already angry, and all that's necessary for the Hulk to come out is for Banner to loosen control.
Also, were people not watching the same movie I was during Iron Man 3? I thought it handled Tony having PTSD pretty well. I idenified at a lot of points with Tony's anxiety and his mal-adjusted coping mechanisms.
And, finally:
Because it's not a damn bullet, it's a guided missile. If he'd just aimed it at the portal, it would have corrected it's course. Also, by the time Tony got it redirected all the way to the portal, the strain on his suit was causing the suit to fail, that's why he said it was a "one way trip", he knew he couldn't redirect the missile and still have enough left to get himself back safely.