I would faint, scream like a little girl and finally i would 吻乐队(Kiss) her and hug her. I would thank her for being herself and ask her a million 问题 before she go.
I would stare at her at first and then ask nicely, " Are 你 Katy Perry?!?!" Then she would say yes. Than I would be screaming, "AHHHHHHHH! I 爱情 you! OMG! I can't believe it is really you!" Then I would hug and 吻乐队(Kiss) her and do all kinds of things with her. I 爱情 Katy Perry!
i would probably squeal at first, then say hi and tell her how awesome she is and how her 音乐 inspires and entertains me, and maybe hug her, if she wouldn't mind :)
I would run up and hug her, tell her how much I 爱情 her and ask her if she wanted to be 老友记 and swap emails so we could keep in touch! If she was upset and cried in front of me, I'd hold her tight and wouldn't let go till she felt better!