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).