Alex
From Rom Com
Alex is a friend of Kati with whom she is very competitive. They come up with a bet which leads him to seduce many people, including at the very least Hallie, Aimee, and at the end Kati herself. His character's name is most likely Greg Mankew.
Alex appears in the following scenes:
Opening
Alex and Kati's Bet
Alex/Hallie Seduction
Photo Montage
Aimee/Alex Seduction One
Dinner Sincerity
The End (Alex and Kati)