Charli xcx, the pop star whose Brat green and Brat attitude have been hailed as defining the mood of the summer, sounded a clarion call this week for the new visible panty line (VPL).

Once an unintentionally discernible indentation running over the bottom, the new iteration is very much on purpose – the waistband of knickers worn above the waist of trousers and skirts.

The image Charli xcx posted on Instagram, in hyperbolic showbusiness fashion, did not just show one visible boxer shorts waistband but three. Commenters were quick to identify the wearer: “BILLIEEEEEE!!!!!!” wrote one, “BILLIEEE NO WAY” wrote another, referring to Billie Eilish, who has made a habit of the visible boxer band and released a remix with Charli xcx.

Even beyond Eilish, impactful underwear is a big statement across pop culture this summer. Troye Sivan, who will be touring with Charli xcx later this year, wore a pair of pink boxers peeping out of checked wool trousers at the Cannes film festival in May. The Euphoria actor Sydney Sweeney paired a Canadian tuxedo with visible white boxer waistband in May. On a recent magazine cover, the South African pop star Tyla showed a slither of yellow Marni knicker above her waistband. On the set of the upcoming film It Ends With Us, an adaptation of the Colleen Hoover book, Blake Lively has been seen wearing patchwork boxers, visible inches above a pair of patchwork trousers, as the character Lily.

“The boxer shorts ‘VPL’ was a conscious part” of the styling, says the costume designer Eric Daman, who has also worked on Sex and the City and Gossip Girl, “striking that unique, unexpected balance between masc and femme”. Lively’s VPL, he said, “feels rebellious and subversive and self-possessed”. He sees the new VPL as giving a “subversive F * U middle finger to societal norms. A strong yet subtle way to show independence, strength and rebellion”.

It has been trickling down from catwalks for a few years. As with many styling vibe shifts, Miu Miu is part of the conversation – the buzzy brand continues to buck the trend of the slowing-down luxury sector with rising sales. Recent collections have featured numerous visible waistbands, and more complicated multiple stacked waistbands stitched into one.

Now the look is so entrenched that trousers, including from Berschka and Zara, come with a boxer-type waistband stitched in above the actual waistband, aping the appearance of a pair of boxers poking out the top of trousers.

As much as it is of the moment, it is also retro. “The latest trend for visible underwear waistbands was actually kicked off in the 1980s by Calvin Klein,” said Iain R Webb, a professor of fashion and design at Kingston school of art. “Before Marky Mark [Mark Wahlberg] and Kate Moss dropped their baggy chinos to expose the CK llogoed waistbands on their jersey boxers, Olympian Tomás Hintnaus posed on a giant billboard high above Times Square in just his CK Y-fronts.”

He added: “It was a moment when the cultural gaze flipped to overtly sexualise the male body, a mood that taps into modern-day thinking around gender identity, roles and stereotypes.”

A lot has been happening in the underwear space in general. A crisp pair of boxers as shorts has become a fixture in the womenswear summer cannon in recent years. The cutting-edge men’s shorts this summer, as modelled by the likes of Paul Mescal, have been short and not unlike boxers. Underwear as outerwear, pants as party outfit; last year Miu Miu championed pants worn over tights – a look that celebrities from Emma Corrin to Beyoncé jumped on. The fever continues with knickers under sheer dresses now peeping out – see the set of And Just Like That, where Sarah Jessica Parker was recently pictured in black undies beneath a translucent Simone Rocha design.

Shaun Cole, an associate professor of fashion at the University of Southampton and underwear expert, sees the visible waistband as “coming out of hip-hop culture and particularly associated with brands like Calvin Klein and Tommy Hilfiger”.

He draws out a difference this time compared with the 90s and 00s: while Calvin Klein marked a kind of bellybutton-height billboard, today “there is less branding visible”.

There is also more of a gender fluidity to the way the look is being worn. Where Marky Mark famously clutching his crotch in a CK advert in the 90s was playing with archetypes of heterosexual masculinity, now, said Cole, “we’re seeing what might be seen as traditionally men’s underwear worn on cisgendered women or on people who are more fluid in their approaches to their gender and sexuality”.