Britney Spears' Most Defining Moment?

Britney Spears. (Reuters)

Believe it or not, little Britney Jean Spears turned 30 years old on December 2.

Yup ... it's been almost 13 years since she redefined the school uniform with her sexy schoolgirl video for "...Baby One More Time" in 1999.

A year later, Britney famously shed her good-girl image (did she ever really have one?) when she stripped down to a nude body stocking at the 2000 MTV Video Music Awards. She topped that by kissing Madonna, marrying her childhood friend Jason Alexander for 55 hours (no, not the guy from "Seinfeld") and marrying Kevin Federline a few months later.

SODAHEAD SLIDESHOW: See Britney's most defining moments.

But following her split from K-Fed in late 2006, Britney spent time in rehab, shaved her head and attacked a photographer's car with an umbrella -- pretty much hitting rock bottom.

Now, after a rocky few years, the former Mouseketeer is back on track as she enters her thirties. She has a boyfriend -- former agent Jason Trawick (they're rumored to be talking marriage and babies) -- a new #1 album, "Femme Fatale" and she won two VMAs over the summer.

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From "...Baby One More Time" to that unfortunate umbrella incident, let us know: What is Britney's most defining moment?