Taylor Swift is the last person who you expect to be starstruck. She brought out Lorde and The Weeknd during her 1989 concerts this past weekend. She is dating producer-DJ Calvin Harris, and she spent her July 4 with supermodels and two Jonas Brothers, who all decided to wear American flag onesies. Yet when she brought out Jason Derulo last night (July 14) to sing his hit single "Want to Want Me" at her Washington, D.C. show, she could barely contain her excitement when he peeled off his shirt. Swift's surprise face appeared to be genuine, which is kind of shocking. If she listens to Derulo as often as she claims ("Want to Want Me" is her "summer JAM," though she likes "Cheyenne" too), she should know by now that he has appeared barechested many, many times before. Watch below.