This is from WORKING WOMAN, March 1984, pg. 122:
YAP: IT'S MORE THAN PAY SPELLED BACKWARDS
Remember when success wasn't something you dressed for? When people ate
Sunday dinner instead of brunch? When the fast track was for express trains?
Well, those days are as dead as the era of dashikis and long hair. Walk
around at lunchtime in any fair-sized city in America, and chances are you'll
find yourself surrounded by Young Aspiring Professionals (YAPs), who are fast
becoming the emblem of the 80s. (In fact, you might even be a YAP yourself.)
by C. E. Crimmins
What's all this about YAPs you may have been hearing lately? Well,
typical YAPs are 25 to 40 years old, well educated, well motivated, well
dressed and well exercised. You may be one yourself. Try taking the YQ (Yap
Quotient) test to see how fast you've tracked to YAPpiness. (...)
YAP borrows from JAP (Jewish American Princess) as well as YIP (Youth
International Party). It's "PAY" spelled backwards!
Perhaps some people didn't like the fact that "YAP" also means someone
who talks a lot. So it got changed to--yes--"YUP" (Young Urban Professional).
The earliest "yuppie" citations are in January 1984, but if this article
appeared in the March 1984 monthly, it was on the stands in February 1984 and
written in either January 1984 or December 1983.
Time to hit the old Nexis for "YAP."