a) tell my parents she's having sex with her boyfriend (and ex-boyfriend) regularly (my uptight azn parents would totally flip out and kill her)
b) throw away the key to the drawer where she keeps her life savings
c) scrub the toilet bowl with her toothbrush
d) other (comment!)
Sadly, I'd never actually do any of these things, but it's nice to fantasize.
eta: To clarify, I'm pissed at my sister, not just randomly taking it out on her.