Spray paint technique that causes the line of paint to widen and fade away. To do a flare you just use your wrist to tilt the can away from the wall. Some caps work better than others. Sunset from france has the best flares, google him for a better visual.
Cope2 has some nice flares on his handstyle.
Person 1: Do stock caps flare?
Person 2: No. Not at all. Go die.