Why do guys my age get touchy?

I have mostly guy friends. I don't have any "feelings" for any of them. I'm the only girl in the group, so some jokes are ok, I'm a big girl. I'm not a very sensitive person.

I just want to know why:

one insists on taking my stuff and hiding it from me

another takes my stuff and always brings it out of my reach (he's really tall)

another grabs my hand a lot and tries to get me to touch him in some places that I don't want to touch (I hit him every time)

another wants me to be by him all the time and even sit on him

another grabs my hand during class and just doesn't let go

another calls me "mommy" or "sissy" and always lays on me on the bus.

That's not all the guy friends I have, but the others don't do anything like that. If it helps, the youngest one of these guys is 12, the oldest being 15, and I'm 13. None of them have girlfriends at the moment, and I don't have "feelings" for any guy at the moment. I just want to know, why do these guys get so touchy, and constantly?