I'm known to carry a bit of water in my mask and slosh it around when I sense fog in my mask.
Fun revived thread
I had to take it out of context, but here is my winner from last years poll.
As one of the early snowboard bums (ex-ski bum) I can tell you about defogging. That's what you do after you get fogged.
For antifog we are lucky in Hawaii; many of the dive sites have a legendary plant with a waxy juice that works really well. So well that my BDB now sometimes has a stash of fresh leaves when we go to a site without naupaka makai.