Man, if it was 1981, and you didn't have a pair of tight-fitting Jordache, Sergio Valente, or Calvin Klein jeans, you just weren't cool, certainly not stylish.

Designer jeans were based on a simple idea--take blue jeans, the quintessential dress down item, and make them fashion statements. This was done by making them out of darker denim than, say, your Levis, using brightly colored thread to stich them together (usually yellow or white or silver or some such), and of course, putting a different stiching detail on the back pockets than the usual Levis chevron. Oh, and while you're at it, charge twice as much for them as you did a pair of Levis or Wranglers or Lees.

Hideously popular from about 1980 to 1985 or so, then the bottom fell out, so to speak, and they just faded into the background (also, so to speak.)

It's interesting to speculate that the popularity of designer jeans has led to things like casual Fridays and the acceptance of blue jeans as more dressy clothing instead of merely work clothes.