You were expecting a bouncy castle?
In a relatively NSFW photo she posted to her Instagram, the 22-year-old "Wrecking Ball" singer is seen with pal Katy Weaver on the gizmo -- a raunchy twist on the mechanical bull.
Cyrus's new beau Patrick Schwarzenegger attended the party, but there's no word on whether he took a spin on the device.
Some outlets had fun with their headlines: "No Bull! Miley Cyrus rides mechanical penis," the New York Post headline blared.