Among fans of certain 1960s-1990s bands (The Grateful Dead), used when something or someone is held in high regard. Don't know exactly what it stands for (I've asked), but Fine and Tasty, Fantastic and Terrific, Fabulous, Awesome and Tremendous would fit the
bill.
Adj : From drug slang, so it may be comparing the thing or person to high quality
marijuana. "Fatty" is used in the same manner.
Adj : In drug slang: a marijuana cigarette or joint containing high quality
marijuana (possibly itself originating from the acronym FAT).