What is WITH this guy?

There is this guy at work, Gene, who is a complete JACKASS.  When I first started at the store I'm at now, EVERYONE warned me about him, saying he'd ask me for my number because he likes white chicks and I fit the bill perfectly for what he looks for.  I pretty much like to make up my mind when it comes to people, so I gave him the benefit of the doubt, and for the most part, he didn't speak to me at all.  I just said, "Hey, how ya doin'" to him, just I do to everyone else I come into contact with and didn't really talk to him at all unless he asked me a question.  He's a quiet guy, keeps to himself most of the time, so I didn't really have to deal with him.  He asked me once if I was married, and at the time I was, so I said yes.  Then Andy and I split up, and Tom and I were a couple and he saw us together and he asked me if I was seeing Tom and I said yes.  Then he said to me, "I thought you said you were married."  I said I WAS. 

One day, not long after that, maybe a day or two... he asks me what I see in Tom.  So I told him.  Tom has a good sense of humor, he makes me laugh, he has a good personality.  I didn't gush over Tom, just stated the facts.  Then Gene started acting like a complete asshole to me.

I don't understand what I did to HIM that caused him to act like a jerk to ME.  I always treated him with the same respect that I do everyone else.  Now he's throwing MY freight on the floor, when I'm putting HIS on his carts.  He's making snide comments about Tom in front of me and just plain being a douchebag.  I said several times since he has been a fucktard to me, that I hope he DIES a virgin.  I hope he NEVER gets laid.  I also said I'd BUY the bullets for the gun so he can shoot himself.  (He is always telling the guys at work, the ones he does talk to, that he wants to kill  himself.)  I know this is terrible of me to do, considering the guy has low self-esteem, but damn... I didn't DO anything to him for him to treat me the way he does.  I always go out of my way to help EVERYONE in the store, including him, get all their work done and to have him do me the way he does just chaps my hide.  He had me cussing up a storm last week, in front of 3 other co-workers, not at him per say, but at the way he was acting toward me.  I hate feeling like that about people I work with, but this one really pisses me off.  (Well, he pisses everyone off... not just me.)