Wikipedia: Happy Slapping
Brief article explaining the criminal act of slapping or striking a stranger while someone films the assault using a camera phone or smart phone.
en.wikipedia.org/wiki/Happy_slapping
Urban Dictionary: Happy Slap
Defintion of the unfortunate London phenomenon where some yoot slaps a random person while recording the act with a camera phone.
www.urbandictionary.com/define.php?term=happy+slap