Katy Perry has become a leading diva because she presents pop tropes head-on with sincerity and a good sense of humor. Her best singles acknowledge that mainstream music should be fun: enter the bubbly disco of "Birthday." Playing with double entendres about party accoutrements, the song bounces along with Perry's signature playfulness. Of course, the track is a master-class in playing with Top 40 cliches: the chorus is sweet and direct ("But when you're with me, I'll give you a taste. Make it like your birthday everyday!"), the perky production feels appropriately celebratory, and the faux-Marylin segue to the bridge about the singer's "big big big big big big balloons" is a good wink at the camera. "Birthday" is the kind of confection Katy Perry has done so well since Teenage Dream, and because she is not afraid to have fun, her music remains a delight.