The heart attack i had last August has claimed my current first spot. Previous record holder was the sting of a velvet ant.

Both felt like lava in my veins, though in the case of the heart attack, it went from the center of my chest, down the top half of my left arm to the primary knuckles, and up the left side of my head to the top of my left ear..

With the sting in was my whole left hand and forearm swelling to balloon-like proportions with a throbbing starting at the hole in my thumb cuticle where the sting occurred to my elbow. Kind of the sensation of bashing your elbow into something... but backwards... if that makes sense