Millennials, for their part, are grateful to their successive generation's penchant for leggings because they, too, obsessively wear them to grab a cup of coffee, for school dropoffs, even to work. And whatever the teen consumer powerhouse still likes is what retailers are keeping in stock.

But now, Gen Z is showing that, even in leggings, "skinny" is almost done. On TikTok, they've been swooning over "flared" leggings for months, otherwise known as yoga pants.

"From a teen perspective, Lululemon is still a No. 1 brand with high schoolers but there is a nod to baggy trousers, pants and leggings now in their wardrobe," said Erinn Murphy, managing director and senior research analyst with Piper Sander.

And for those teens who still wear skinny leggings, they are styling the look as a "triangle" or "inverted triangle, she said. "So its baggy t-shirt with skinny leggings or a shorter top with a looser pant," said Murphy.

Pacsun president Brieane Olsen said the push for loose 70's flares and 80's baggy styles in pants and leggings is dominating Gen Z, and the styles are popping up heavily on TikTok and Instagram reels.

Consequently, she said, "at Pacsun we're seeing a sizable shift into looser silhouettes in bottoms across both our men's and women's consumer. Wide leg, loose fit or baggy, flare and super flare, and boot cut are surging denim trends with our Pacsun consumer."

Olsen went as far as to say that skinny pants have begun to lose currency with Gen Z over the past few years, and "going into 2022 will become close to obsolete for our consumer.

Market research firm NPD Group noted in a recent report that consumers overall have adopted more casual and cozy fashion styles "from head to toe."

In the women's jeans and active bottoms categories, such as leggings, looser fitting styles are gaining share, said Maria Rugolo, fashion apparel analyst with NPD Group.

"We are starting to see some looser fits in active apparel, as well," she said. "Flare is the style right now and TikTok is having a moment with it."