I studied video production in college. For one project, I did a documentary on a non-profit that was working in a high-crime area. We drove down the street with a video camera pointed out the window * As we drove by a house with some young men on the porch, one of them saw the camera and yelled angrily, "Yo, what the fuck!" and started chasing us. After that experience, I've never been able to point my camera at someone without getting their verbal consent first. I worked for awhile as a photographer/videographer for a school, and struggled to get good footage of students because of that.
* (With the documentary, we hadn't intended to record and people without consent, and when we finally published it, we had signed consent forms for everyone who appeared in it.)