Peggy's vibrant lipstick -- before it gets smeared all over her teeth. Photo: Courtesy of AMC

Thanks to the uber-influential Fall 2010 collections by Louis Vuitton and Marc Jacobs, the below-the-knee circle skirt is back in a major way this season (see Louis Vuitton's '50s-style ads here).

Want to know how the ladylike style was worn back in its heyday? Look no further than last night's episode of "Mad Men."

Starting with the first scene, the skirt is in full display on Peggy, who wears a pale blue version and a red-and-white-striped tank over her thick one-piece bathing suit, all paired with a head of wet and disheveled hair that we found particularly charming.

A fitting style for the conservatively dressed Peggy, the loose skirt pops up on the ambitious copywriter twice more, once in a light olive tone worn with a pretty blue and brown patterned tie-neck blouse, and again in the form of a navy blue dress with two wide cheerleader pleats that split to reveal bright orange fabric.

In the latter, Peggy has a rather cringe-inducing moment when she goes through an entire presentation for Platex gloves with bright pink lipstick streaked on her teeth. Yikes! (Make sure to avoid such mishaps when you're trying out these top 15 lipstick shades for fall.)

Back on the circle skirt front, Don's secretary Megan pairs a rosy pink version with a white blouse embellished with an orange and pink neon floral print before, um, having it all ripped off by her insatiable boss.

Naturally, a circle skirt silhouette isn't exactly curvaceous office manager Joan's cup of tea, but she stuns nonetheless in a carrotlike head-to-toe blood orange look (orange skirt, orange blouse, orange lips, orange nails) that match her red tresses to perfection.

However, that doesn't mean Joan is immune to wearing comfortable clothing from time to time. When Roger makes a late-night visit to his bodacious employee, we get to see her in her nightie -- which, surprisingly, isn't frothy or frilly, but a chic pair of blue-and-white-striped men's pajamas that make us love her even a little bit more (if that's possible).

In related news, read about "Mad Men" costumer Janie Bryant's QVC collection.