I've been running across the word phat, which from its context seems to mean something like cool or groovy. I'm wondering where it might have originated.

I guess we're gonna have to defer to our token young'un on that. Jazzoctopus by name. I've heard the term but ain't got a clue.

My coin would be on BY's quoin for this coinage

In other words, your money is on the coiner piece? [wunk]

Well, I'm not as young as Jazzo or BY, but I am young enough to know about phat. Phirst of all, it's already on the way out (off-the-hook or off-the-chain is a more up-to-the-second way to say "cool" -- it's a reference to meat, by the way). The AHD (yes, it's in there) says that the origin of "phat" is unknown, but notes that it used to mean "sexy". Apparently the word has been around in that sense since the 60s, and I have heard that it derives from the acronym Plenty of Hips And Thighs, but as most acronym-based etymologies are not true, I tend to doubt this one, too. I'll do some more research, though.

Phat at first glance is a virgin slang word, an inventive
new superlative (meaning either sexy or cool) conceived
of and delivered in the rap idiom of the hip-hop culture. In
the Fall 1994 issue of American Speech, John and Adele
Algeo postulate that phat may have been devised as an
acronym for "Pretty Hips And Thighs"; others have
speculated that it was drawn from "physically attractive."
If you forget the cute spelling, though, and look at fat, the
explanation is probably a lot simpler.

Well, I have teenagers: Pretty Hot And Tempting.

Pretty Hot And Tempting.

yeahbut®

could that be the sort of post-facto rationalisation that we also see in people seeking for acronymic etymologies so readily?

Well, I read it in one of the magazines my dau. likes to look at (I like to try and keep up with what they're interested in.). I have no idea how it got started.

Pretty Hot and Tempting it is.

I remember it from a movie with Martin Lawrence (spelling may be wrong) as star. I'd don't remember which one though. I remember it was in the late 90's though.

He looks at this biddy and says "you are phat". She understandably looks around all started and on the verge of getting really angry and he says "pretty hot and tempting"

Pretty Hot and Tempting it is.

Is it? In my experience, only things or events are phat. People are only phat for the sake of a cheap laugh. In my circle, phat tends to be used rather tongue-in-cheek, usually to describe something/someone who is trying to be cool, but failing. As with all words which originally mean good, it has come to mean bad.

I think I am decidedly "not with it" when it comes to youngster expressions. It may have changed definitions, as most of these type of expressions do.