SmileBomb

SmileBomb a stranger, or frown if you must. Hold your iPhone in front of your face in landscape mode, screen side facing away from you, and let other people see how you feel. A high tap on the screen brings smiles, a low tap shows frowns, and signal beeps let you know what you're showing without you looking at your screen. Swipe left or right to change faces, from cartoons to caricatures, from monsters to cats.

Point at a clerk in a checkout lane to flash a smile, or smile at a friend from accross the room. You can even SmileBomb in a photobomb.