It's Midwinter, and a Hearth's Warming celebration like no other... and Celestia is trying to sleep.

With Luna freed, she wants to let her hair down. She does it in the royal ballroom on the longest night, her night.

Big party, free booze, what could go wrong?

This is the Applebloom Safe version. Unshorn Fetlocks version is... elsewhere.

EDIT: Since it's linked in comments, I'm marking this mature.