A piece of glass or other sharp object found on the ground in a naural setting. Since hippies have the tendancy to walk around bare-foot, these objects readily spread tetanus or at least "really harsh their buzz."
Someone threw a beer bottle into the campfire, leaving a few nice hippie killers behind.
A second rate, badly designed wood burning stove made of too thin metal and with bad castings and welds. A classic method for back to the landers with more desire to live the natural life than money to get outfitted properly to get burned out of their funky hovels.
The Flower Kids were living in the back forty but their hippie killer blew up and torched their shack