The pop singer held a large photo of Gomez's head taped onto a cardboard cutout of a woman's body wearing fishnet stockings, a bra and what appeared to be no panties, then she threw the paper doll into the audience.
The photo was thrown on stage by a fan, and as Miley danced with it she held her microphone with her middle finger stuck out (see photo at E! Online).
That's not all -- Miley was singing her latest single, "FU," a the time.
No clear motive for a feud between the two stars has been revealed, although a source close to Miley told E! News that the two have bad blood dating back "to their Disney days" because both dated Nick Jonas.
"Things turned sour after Miley broke up with Nick Jonas in late 2007," the source said. "The following year, Nick began seeing Selena and that is when the beef blew up.
Additionally, Miley's been hanging out with Selena's ex Justin Bieber a lot lately, according to reports.