Theory. You know how when it's cold out and you have a scarf over your face but you can still see your breath? VFT is a theory that when you fart outside in the cold that you can see a puff, if you're wearing thin enough pants. Until I actually see it for myself, it's still only a theory.
There was someone walking behind me last winter. It was so cold I was afraid to fart because of VFT.