Costume ideas 4 2 girls at halloween?

me and my friend are freshman and we're going together as halloween. we kinda wanted 2 go as a pair but we dont know what 2 do. my friend is kinda shy and i'm all like we should be paris hilton and nicole richie or we should be britney and k fed and she's like NO. so idk what should we be? and just in case we decide 2 go with our other 3 friends what should we do? i need group and pair suggestions.