Spitback is the name for the occasional super-hot droplets of e-liquid that shoot up at you when you’re vaping. If you watch an RDA coil firing, you can sometimes see this happening, usually accompanied by popping sounds. The droplets spit in all directions, but if you’re unlucky when you’re vaping, one will shoot up into the mouthpiece.
Spitback has a simple cause: e-liquid gets pooled up on the coil itself and gets “cooked” instead of being vaporized. This bubbles and spits in the same way a pot of boiling water does, and with you inhaling from the tip, you can easily suck up a droplet or two. The problem is closely linked to flooded coils, but in some cases it can happen even without flooding.