I thought this was just an urban legend, my advanced instructor warned me about it. I had just flown, landed and refueled, I had a 13 year old student I was telling this to and I gave the prop on one of my YS engines a flip just to build tank pressure and it fired up without any heat on the plug.
That pair of pants was a throw away!!!
Only time I had seen it happen but I now know it isn't just a legend.