Some part of Baltimore.
If you taking 95 from Philadelphia to DC, do NOT try to use Route 1 to get around the gridlock, especially if you are driving late in the evening . It will take you through some nasty parts of the city .
Most of Macau, outisde of the casino area is pretty miserable. Plus they have the most poluted air I have ever experienced. You can feel it the minute you step off the ferry.
Lyon, France - beautiful city and amazing food. At the same time, lots of bored looking teens, trying to stir up trouble. I've been all over, but this was the only time I've had to run from a group of people, one of which was holding a surpisingly large knife.
Oh yeah, some parts of DC can be nasty as well, but they are easy to avoid.