An UWS fashion statement

Today I saw something I'd never seen before, and was wondering if this happens a lot, or if this was more of a once-in-a-lifetime sighting: An older woman was sitting at an outdoor cafe with an older man, possibly/probably her husband. She was wearing a sports bra and no shirt. That's generally not done at outdoor cafes in that area, even by the members of the neighborhood's yuppie singles' scene, so seeing an older, presumably attached woman dressed this way was a bit unusual. More unusual still was the cloth napkin she had tucked into the elastic at the bottom of her bra, such that her stomach was just about entirely covered by the napkin. It was a summertime version of the classic napkin-tucked-into-shirt look. As I said, I'd never seen this done before, so I'd like to know if this is the new thing, or if what I witnessed was just garden-variety Upper West Side eccentricity.