Ashton's girl at the wedding? SPOILERS

In the scene where Ashton and his friends go to the wedding, and one of his friend makes the bet with him if Ashton was able to get the girl. So then when he gets her, they talk then afterwards walk outside, and why does she say something about him 'having to pay her money'? Anyone know what she was talking about, why did Ashton have to pay her money? she continued saying it when she got in her car. I didn't get that. Its not like he slept with her or she payed for his drink..so what was with that. IMO she was too bitchy and rude, he shouldn't have stayed with her