When she's not weighed down by dozens of layers of oversized duds and pounds of clunky jewelry, Mary-Kate Olsen can really cut a rug. People reports the pocket-sized teen titan celebrated her 19th birthday by shaking her teeny-tiny groove thing on the dance floor of New York hotspot Bungalow 8 late last week.

According to the mag, Mary-Kate, in a barely there white mini-dress, descended on the club with about a dozen friends (sister Ashley was a no-show) "for a night of wild dancing, champagne, shots and cigarettes ..."

Olsen then proceeded to boogie the night away (the New York Daily News unkindly likened her dance moves to "being Tasered") with an unidentified "dark-haired" guy who apparently wasn't her vertically mismatched boyfriend, Stavros Niarchos III.

While Mary-Kate and her mystery man engaged in nothing more than some platonic hand-holding, she did see a little action on the dance floor. Model Natalia Vodianova reportedly lifted the birthday girl into the air while simultaneously giving her wee posterior a squeeze.

People says the mannequin's husband later toasted Olsen and treated her to a shot, but given that MK is underage, we'll just assume it was a shot of Red Bull.

Later, as she busted a move to 50 Cent's "In Da Club," her pals presented the calorie-averse twin with a pair of cakes complete with frosted rose petals. No word on whether she indulged in the sweets before calling it a night around 3 a.m.

"School's out. Summer's here and they were having fun," Olsen's rep explains to the mag, adding to the Daily News, "Well, it is birthday week."

In related news, is Ashlee Simpson hoping to catch Ashley Olsen's ex on the rebound? According to the New York Post, Jessica's "La La"-warbling little sis, who was last linked to Lindsay Lohan's former squeeze Wilmer Valderrama, was seen getting up close and personal with club owner Scott Sartiano last week in Los Angeles.