I can't help but be cranky?

I'm 19 (and female); I still live at home because it's easier right now. Anyway, my mother is very even-keeled but VERY pive-aggressive and gets extremely upset if I so much as have a slight tone in my voice. My father is explosively angry and verbally abusive. I'm getting crankier and crankier and I've started to show a bit of a temper myself. I feel like I can't help but be snippy and aggressive; it's like I'm constantly in defense mode. How can I solve this problem? Do not suggest I move out. I can't right now.