Quick synopsis:
A hot clubber watches beeps, then she runs off. Then a overweight guy at a computer uses a morphing device to turn into her and dances at the club in her body, the same watch beeps without her knowledge and she changes back in the club to a somewhat disturbing sight.
ALVARO & JETFIRE - Guest List
The transition from him to her starts at about 1:45, the reversion scene is at about 2:35.