@katyperry/Twitter

Katy Perry's been sick, but that didn't stop the singer from doing her patriotic duty and performing Friday night at the U.S. Naval Academy in Annapolis, Md.

In a video posted on YouTube, Perry, wearing a sailor-style halter top, skirt and a Navy cap, calls a sailor named Beasley up onstage for a kiss, but first asks him how old he is. When he replies that he's 20, she responds, "Is this legal? Well, I'm a little bit older than you, but that's all right, I can be your Mrs. Robinson." Perry was referring to the character in the movie "The Graduate," in which an older woman seduces a college boy.

As the audience whoops in delight, Perry tells Beasley, "If I told you I had a cold, if I told you I flew here with a 101.8 temperature, would you still be all right with that?" When he responds, "Oh yeah!" she tells him she wants to recreate an iconic World War II photo of a sailor kissing a girl. "You ready?" she asks. He dips her low and kisses her, while she lifts her knee in the air.

Perry later tweeted a photo of her posing backstage with a bunch of people - who appear to be her band and backup dancers - in naval uniforms. "Played for some Navy guys & gals tonight," she wrote. "I think my fever broke on stage from all the sea-men."