What is a substitute teacher?

Today I substituted. Now, I'm sitting here thinking about exactly what that means. The problem is that I become so emotional with the whole thing. Maybe I take it way too seriously. Here is how it went today.

So I'm sitting there, my nose in a book, not wanting to pay attention even though I can pretty much see everything in my peripherals. The students are so.....squirmy. It's almost like their seats have an electric shock and they just can't sit in them. The teacher doesn't really leave anything to do so they are there talking, to the best of their ability, above each other until it grows louder and louder. I just want to lay down. I'm not feeling so good, and they are pushing me to the edge. Well, they finally do because I yell at them. This happens over and over, with the three grades I sub for in a day.
It's kind of a sad story. One period, everyone practically ignores what I say while one kid is threatening the others, trying to help me, but what he doesn't know is that he is just making matters worse because, one, they don't respect him because he is too old to be in that grade; and, two because I don't respect him because the class before he busts in (in all of his hormone raging, over testosteroned anguish) and threatens to beat the (insert one of the two words appropriate) out of another student. And this is how it goes. These are the students pretty much all the time, and the sad story isn't necessarily all about them, but about me too. Why? Because these are the kids that I first saw three months ago as I bounced through the doors of the school. Yes, bounced, because I had heard so many terrible things about them; yet, I wanted to help them. I really did. Although they are intolerable at times, I really wanted to be there for them and I tried. But, they didn't respond and now here I am in the same seat as everyone else, not hoping, not caring, putting my nose in a book to ignore them because they don't want to care and they don't want me to care. At least it seems that way. So, I'll leave and move on and never think twice about it. Isn't that sad?
And why does it have to be so? I suppose because I am after all just a substitute, not a "real" teacher. I am like the generic, an Equate teacher. The brand name is more valuable, and in all honesty the real teacher has way more work to do. I'm just a babysitter. This isn't so sad though, because I didn't want to be the brand name real thing. I just have to move forward and pray that student will break out of the year after year apathy trend.