Take a litbium ion battery and stab it with a screwdriver. Stand back and do it outside.
Or just look ok youtube. Get 10 Jihadis on a flight, stack the batteries on top of eachother and you have something resembling a thermite grenade.
Hoverboards are likewise dangerous. Have you saw videos of those things blowing up? How the heck did they ever get approved for sale in the first place?