if my memory serves me correctly, pajama parties became popular in the early 90s thanks to the release of the movie, house party 2 (1991). starring 80s/90s rappers, kid n play, play comes up with a masterplan to earn kid's tuition money back - a pajama party where men pay an entry fee and women clad in their pj's enter for free.
i will tell you every tom, dick and harry wanted to throw a pajama party after watching this movie. i wasn't quite in high school yet, but i went to at least two. during that time, dressing provacatively wasn't really our steeze. we still rocked baggie jeans and knee length shorts so no, we weren't wearing lingerie to these parties. we were innocent (ahem, clearing my throat) in flannel (ok maybe polyester) pj pants or shorts and tee shirts. nowadays, these teens ... i can't imagine what they'd rock to a pajama party. enough to make me blush, i'm sure.
check out this scene from the party with toni tony tone singing and a dance off between kid n play vs. tisha campbell (gina from martin) and her friend.