mom.
my dad yells a lot, but it's mostly just hot air... and, I mean, how seriously can you take a frenchman yelling?
my mom, on the other hand, very rarely gets mad, but when she does, your only hope for survival is to either leave the house or stay in your room and be so quiet that she forgets your home.
I've only ever seen her pissed off at my once... and that was when I failed 6 classes in junior high, forged her signature on the letters that were being sent home and on the report card, and she had to find out about it when a teacher stopped by the house because he was concerned about my home situation.