I'm with Lyra on this
At first I was pretty sure that Snape was Slytherin stuff, but thanks to you guys, I am in a Snape-crisis
You sure have good arguements to proof that he could have been in Gryffindor.
I'm more or less with Beatrycze about Snape's behaviour. Of course Snape should behave as he is, but don't forget, he had quite a nasty childhood. He had basically no home: at home with his family there was abusive behaviour and at school it continued. Those are the only two places I see Snape spending most of his time. As far as I know, at home the abuse was not directly aimed towards Snape (although it could be quite possible that his father verbal abused him for crying or whatever), but all that leaves scars. Perhaps that is why Snape got interest in the dark arts to give him a sense of power over others. Don't underestimate the power of bullying. It can have effects for life. Just take a look at reality how bullying can often have a massive effect at the childrens lifes. Maybe what kept Snape on his feet was the prospective that one day he would make them all pay (becoming a Dead Eater and a person of power). If you don't even grow up with a proper set of morals from home, it is easy to start hating everything around you and become bitter.
His hate is so deep that he won't cut anyone, who has any kind of link with the humiliating part of his past, some slack. Not that I approve of his actions (you can't blame a kid instantly while the kid didn't even knew of anything and came in with the best purposes at mind), but Snape has his reasons.
Alan Rickman is not how I imagined Snape (Snape is described in the books as a greasy spider like person, with a hawk's nose, greasy locks hanging in front of his face, etc.) and he wasn't the first choice for Snape, but he's fine. But I'll always like the book Snape more