One major factor is that, yes, that incident of when my former roommate violently assaulted me is still bothering me. By troubled, I mean I'm still outraged that he's free and has gotten away with it completely unpunished despite my having called the police.
I have fantasized quite a bit about taking care of him myself. I won't go into detail because they are rather gruesome and irrelevant anyway. The fact is such an intense state of arousal—whether fear and anxiety, frustration, or anger and hatred as in this case—has the effect of releasing stress hormones (I think cortisone is the name of one such important hormone) which can have lingering effects on the body. Some of the physiological side effects are that I am startled much frequently by even slight sudden noises, have higher blood pressure and pulse, and more trouble falling asleep than usual.
After that attack, whenever I've seen someone who resembles my former roommate (i.e., African-American male dressed in hip-hop- or gangster-style attire), I see it as a violent person—almost no different from Demetrius Tice, the beast that attacked me. At college, before the semester was over, I gave such beasts a ferocious stare to keep them at a distant and frankly I felt the urge to attack them preemptively (à la Bush and his Doctrine of Preemptive Defense, I suppose).
A day or two after the attack, from a distance, I saw someone who looked like he might be my roommate, so I put on the ferocious stare, but it turned out to be this black guy I know who was actually a pretty decent guy. My eyesight isn't the best.
Anyway, he must have been wondering what on earth was going through my head and did return a mean look, probably out of defense.
You learn to conduct yourself as a member of society and are taught that the right way to pursue justice is through our legal institutions. Sometimes, though, even in the United States, our institutions neglect the pursuit of justice, and you're left powerless, unable to do a damned thing to restore justice and protect others who may be in danger, or vengeful, pursuing justice yourself extralegally (and putting your own life and freedom in jeoperdy).
