I think it's mostly because the OP is in south Florida. I've read on both this and the Road Cycling forum how nasty Floridian drivers can be. I even read on some automobile article or message board how they're rated by some poll or study as being the meanest.

Florida aside, I also wonder if you're just commuting through a lousy area. My commute takes me through two upscale neighborhoods and I get no grief there. In different parts of town, though, I can expect different.