She's obvious either still got something for you and wants to make you jealous. Or she's really bitter.
Three things you could do.
1) If you think she still has something for you and you want to get even - approach her, tell her you were wrong, you want to give it one more try. Steal her back from the dude, then use her in front of the him and dump her. If the guy says dick, pound his ass into the ground
2) If you think she still has something for you and you want to have fun - next time they're playing this game, sidle up next to them, put your arm around her and tell her she's still the hottest thing you know. Work for the 3-way. If the guy says dick, pound his ass into the ground
3) If she's bitter - laugh it off, and tell her you're sorry she had to resort to slumming. It the guy says dick, pound his ass into the ground.
And then there's Satanic Goatslayers advice...