what is retrospective lingerie?

Answer 1

Underwear that makes men take a second look back over their shoulders, of course!

Otherwise, it is an attempt, using the wrong word, to describe lingerie in an old-fashioned style. "Retrospective" means to "look back" in the sense of an art exhibit surveying an artist's career leading to the present. It is also used sometimes in an essay form reviewing a person's career, or the course of events culminating in a present condition.

And in this case, it probably means old pointy bras, uncomfortable tight elastic foundation garments, and perhaps some negligees trimmed with mariobou.