Our line in the sand

Each of us has his own line in the sand.  When this line is crossed, we take a stand and fight.  When I say "fight", I'm not talking about sending letters to congressmen or attending protests while holding signs.  No, I'm talking about standing firm against the "authorities" and making it clear that blood will be spilled if any more aggression is committed against you.  Every so often we hear about individuals whose line in the sand had been crossed and that person snapped - but his resistance was futile because he stood alone.