This was on the news this morning. The rechargable lithium-ion battery was loose in his pocket. My guess is that he had keys, change, etc in the pocket as well.
It's a shame that the media will blow this out if proportion and cast a bad light on vaping in general. All because of one individual's stupidity.
Arlington Man Sets Crotch On Fire, Sues Vape Shop Over Exploding E-Cig Battery « CBS Dallas / Fort Worth
I dunno; if a guy goes into a shop and buys some lights and party stuff for a birthday party, the FIREWORKS should come with some big red "WARNING" and "CAUTION" markings