Reese Witherspoon -- Dancing Queen (GREAT VIDEO!)

Reese Witherspoon was the funnest girl in Capri, Italy Wednesday ... rocking out the way only white girls can during what looks like a wedding-related event.

Reese whipped her hair back and forth -- champagne in hand -- as she rocked out to "I Will Survive."

It's unclear how many times Anema e Core - The Tavern refilled her glass, but we're guessing several.

Judging from the video, she had enough to get footloose, but she was not "beyond."