Dressed up in a tiny Elmo tee and an even tinier plaid skirt, the "Hot N' Cold" crooner bounced her way onto the show's Bronx Beat set as Maureen DiChico, a neighborhood library volunteer whose attire was a bit too biblio-bodacious for kids attending her storybook reading sessions.
"Who cares if kids are looking at boobs, all right? Boobs feed babies," offered Rudolph.
"You do your thing at the library. The kids come for the boobs, they stay for the books, everybody wins," Poehler quipped.
Perry, who tweeted "prepping for some Saturday Night Live-ness…so excited, ohhh myyy gawwwd, all my favorite girls are in the hallway" prior to the show, went on to perform "Teenage Dream" and "California Gurls" after the sketch.
Take a look Katy Perry's hottest red carpet looks in our gallery!