Katy Perry appeared as her real self in Season 22's Christmas episode 'The Fight Before Christmas.' Structured much like the 'Treehouse of Horror' episodes, this episode took place in four parts instead of three, and Perry doesn't make her appearance until part four.

In the final segment, everyone has changed from cartoon form to puppet form, mocking 'Sesame Street.' You see, Katy Perry appeared on the children's show prior to her 'Simpsons' stint, and she was criticized greatly for wearing a cleavage-flaunting getup on the children's show -- this was her way of sticking it to the Muppets and brushing the incident off her shoulders.

In the episode, the Simpsons are leaving for a trip to Hawaii and are trusting bartender Moe to take care of their home, along with his girlfriend Katy Perry. But it's the rousing rendition of '39 Days of Christmas' with Perry's red leather dress featuring 'The Simpsons' faces on it that's truly the most memorable part.

 

Watch Katy Perry's Cameo on 'The Simpsons'