To get this effect, I sprayed a line of whipped cream into a bath of liquid nitrogen for 5-10 seconds. The cream is very light and fluffy and full of air, so it freezes almost instantly. I found that by rolling the frozen cream around on my tongue while chewing very gently, massive amounts of vapor would shoot out of my nose and mouth. It's speculated that there may be a danger if large pieces of cream are eaten, as it could quickly shock-cool the mouth and cause tissue damage and/or microfissures in tooth enamel. To avoid that risk I just roll the cream quickly on my tongue. If you roll it fast enough, it doesn't even feel cold at all. Assuming that my mouth is approximately 98.6F and liquid nitrogen is -321F, there is a difference of nearly 420F.
As the super cooled cream contacts my mouth, it instantly condenses my breath into water vapor, and that is the fog you see coming out of my nose and mouth. I highly recommend having a warm drink within arms reach so you have a way to warm your mouth back up, just in case it gets uncomfortable for any reason. Again, the majority of people won't have access to liquid nitrogen, and those who do should be familiar with the risks associated. I do not recommend anyone actually try this, I only say that this is what happened when I tried it for myself. :)