Trending Cute Black Coffin Nail Ideas / They're called ballerina nails or coffin nails because the shape resembles both a coffin and a ballerina's slipper. Coffin nails range from short to long in length, are tapered at the ends, and are squared off (like a coffin). Cute Black Coffin Nail Ideas : With thousands of pins on pinterest, it seems that i'm not alone.