Don't Flash Headlights??
According to an article in the Orlando Sentinel, you could be in trouble if you flash your headlights to alert another motorist that they are driving without headlights. Of my own knowledge, this has been a courtesy of the highways at least for the last 45+ years. According to the story (by Jill Duff-Hoppes) this has become a topic of conversation at local schools and community meetings.
This story is about gang-initiation rituals, involving driving around without headlights on, then the first driver to flash their lights becomes the target and is chased by the others and shot at or into the car.
The full article is certainly worth reading. You may have received something similar by e-mail if you use a computer. According to the article these rumors have spread around the United States for years, popping up in different places.
Check this site: http://www.orlandosentinel.com/news/120598_LORE05.html