Sienna Miller and her boy Rhys Ifans flew into Mexico City Airport late last night and boy do their arms look tired. Groan. These two are pretty inseparable these days, much to the chagrin of another of Rhys's good girlfriends, Kate Moss. Kate, who doesn't much like Sienna anyway after she dated Kate's friend Sadie Frost's ex, Jude Law, apparently threw a bit of a fit before Davina Taylor's birthday party over the weekend. She's also rumored to have threatened Sienna if she ever even thinks about hurting her friend Rhys. Feisty. Maybe these two beautiful women should stop fighting with each other and focus on their own projects — Kate's holiday line at Topshop is out and Sienna just signed on for an exciting new movie role. She's the first official cast member for the upcoming G.I. Joe movie. Watch out Kate, sounds like Sienna's going to be getting into fighting shape.