Good question....the word came from some guys who felt they were being placed in the "jungle" due to them not being welcomed to smoke in public.
They came up with the word "FOG", Freakin Old Gorillas...and the word just stuck.
Its kind of like a bunch of gorillas getting together for a herf...someone just said I'm going to herf some cigars tonite and the word stuck. Nowadays when someone announces they are going to have a "herf" it just means a couple of FOGs are going to get together and smoke a few cigars and just hang out.
Silly I know...