Halloween Costumes for 2 "Girls"?

My friends and I through a bit of trickery are going to be able to dress 2 different guys up at Halloween. They both were putting women down in a sociology cl and we decided that this could be a great bit of payback. Neither one knows the other one will be doing this and they are both rather slight so we thought we'd give them a theme to make it even more fun. So far we're a bit stuck. We've come up with Britney and Cristina, Nicole Richie and Paris Hilton, the two girls from Abba, 80s Madonna and current Madonna, or the Olsen Twins. We like Nicole and Paris the best, but other than the dog we couldn't come up with actual costumes. Any ideas for that costume or easier to manage famous pairs?