The Concise New Partridge Dictionary of Slang and Unconventional English (2008) says:
Gucci adjective stylish, especially cleverly so. From the high-profile fashion brand UK, 1995
Searching Google Groups, here's a 2000 post to a Straight Dope Message Board thread on "Gen-Y Slang":
CLASSIC = stylish, "Gucci," hip, awesome
And a 2001 post to a alt.military.uk thread on "Contemporary British Army slang"
scran= food, tab=ciggie, gucci=showy or flashy, i'll think of some more later
It's quite hard to search for early uses other than in slang lists. However, when searching for bicycle-related posts, I found this February 1994 post to rec.bicycles.misc titled "Cycling jerseys. Are they better than sex?":
I was kicking around the idea of getting one of those slick
looking cycling jerseys with the gucci rear pocket.
That was until I saw the price tag on these thinks. Anything
from $80 to $200, depending on how stylish you want to
look and whose product you want to advertise.
(Someone later replied: "Well, I don't really think it's a gucci pocket... ")
Whether this is the same use or not, the slang use is widely later used for mountain bikes from 1995 onwards.
From a July 1995 post to rec.bicycles.off-road:
You also seem to have a problem with my riding position...so what if I
ride with my head on the bars!!! Well mister, next summer I'm teaching at
the Colorado "How to ride your Gucci Mountain Bike better" summer camp.
There's going to be a whole wave of riders emerging with their heads
firmly planted on their handlebars.
An August 1995 post to rec.bicycles.marketplace was titled:
Gucci parts For Sale
An 8th November 1995 post also to rec.bicycles.marketplace titled "FS: DEAN Titanium MTB frameset 19.5in. $800":
Also available: Mag21 SL TI long travel suspension fork $225
many other components available, just ask!
bike could even be sold complete with loads of
And a week later to the same group, a reply to "Lots of High-End MTB Stuff For Sale":
I am interested in many of your bike parts but need more info. [...] How did you end up with so much gucci bike junk?