YouTube pranks seem to be a popular thing for “bored” youth to do, but one video prank of snatching cell phones out of the hands of unsuspecting targets is met with some hostile responses. Earlier this month, a video series of two brothers trying to swipe strangers’ cellphones surfaced online. What differentiated the shorts from your average YouTube prank was the unsuspecting target: African-Americans in a poor Brooklyn, New York, neighborhood. The videos—which immediately went viral and have drawn more than 1.5 million hits—generated a furious reaction, including death threats aimed at the filmmakers, Moe Etayyim, 20, and Et Etayyim, 21, of...