What are some easy, free stress relievers?

I have six year old little brother who everyone thinks is a saint. When in reality, every time my mom leaves the house for more than two minutes, he is demon spawn. I ask him to stop doing something, like terrorizing the cats or making loud noises and he either mimics me or finds some way to get me in trouble for telling him to stop. I've tried to do something about and I've tried to get my mom to do something about it (no, my dad does not live with us.) So, now that you know why i'm stressed maybe you can help me unwind?