What is that movie about a sorority and...?

the only thing i could remember is that this girl was rushing the sorority and all the girls needed to find a guy on the campus to go to dinner or something. that girl couldn't find anyone except a nerdy guy (don't think it was a fraternity guy). all the girls then went to dinner even with the nerdy guy. then the sorority girls told that one girl to ditch the guy and the nerdy guy had to pay for the meal or something. that's the only thing i remember. sorry if it is poorly worded ):