The state of being casually, sociably or lightly buzzed for inordinate amounts of time, e.g., a few days. Permafrosting usually involvs drinking upon waking up, and continuing to do so into the night (see: wake'n'drank.) Usually done on weekends or short vacations in foreign countries with a warm climate.
"Doesn't that gentleman look jovial?"
"Yes, I believe he's been permafrosting."
"Good morning Ms., care for a cocktail?"
"Let us permafrost."