Britney Spears Shares Extra Naughty Valentine's Dance With Some Spanking

Britney Spears celebrated Valentine's Day with a dance video ... which usually wouldn't be anything out of the ordinary -- but this one got pretty naughty!

Brit posted the vid Friday night ... doing her dance in a practically see-through lacey black top and thong with matching black boots and a hat.

As she has done in several dance videos ... she rubbed along her toned body, making sure to highlight her assets -- but she added a little extra for V-Day when she spanked herself a few times before nearly pulling down her thong to show full-on peach!

There was no caption for the vid ... and Brit turned off the comment section ... but she sure seemed to be having a good time being an epic tease on the day of love.

Earlier in the week ... TMZ broke the news Brit's old Beverly Hills home -- where she was famously stretchered out during her 2008 health troubles -- is on the market ... and it’s packing one serious price tag!

For a cool $7.99 million, you could own the 6-bedroom, 7-bathroom estate -- a luxury oasis in the 24-hour guard-gated Summit community, complete with a soundproof screening room/music studio, plus all the other usual high-end perks.