In video of the backstage gathering, the 23-year-old Swift looks annoyed when the two stop for a catch-up session, while another friend tries to pull Gomez back into the crowd.
When Gomez wraps her arm around Bieber and grants him a kiss on the cheek, Swift sticks her tongue out.
Here's the GIF, courtesy of Zap2It:
The moment occurs at the 1:00 minute mark below:
Seating arrangements at the musical event fueled speculation that Gomez and Bieber might have rekindled their relationship, though Gomez told a radio station last week that she was "completely available in every way."