I'm definitely prejudicial towards young black males. Every crime that's ever been committed towards me or any place that I worked was by a young black male. Thus, I think it would just be stupid of me not to face up to simple statistics and realise that I'm more likely to be mugged by a black guy than any other race. Do I think this is because of some inherent inferiority? Of course not. But because of social situations in my area, yes, blacks certainly are most likely to committ a crime. So, when a group of thug-looking black kids comes into the place that I work, I keep an eye on them. If it turns out they're nice kids, great. I'm not prejudiced to the point where I'll refuse to be friendly with a black guy - My two closest friends are black - But yeah, I'll assume worse things about a black person at first glance than a white person. And I don't feel any particular guilt about that. Young black males, as a group, have failed to give me any reason *not* to be suspicious. Similarly, if I see a guy with green hair, I assume he's got absolutely nothing of any importance or interest to say, because, well, they rarely do. I've been proven wrong once on this though, and ended up befriending the guy. Still, it's been proven right many times, and I'm sure I've dodged some unpleasant conversations because of this prejudice.
Black females, no problem. Old black guys? Some of the coolest people as a group that you'll find.