The `Firework` singer - who split from husband Russell Brand in November - was asked if she would ever collaborate with her close friend and though she ruled out working on a record with the star, she joked that they would do something more intimate instead.
She joked to US radio station Wild 94.9: "No, but we`re going to have sex."
Katy was also asked if she listens to her own music when she is having sex and said it would be "over the line".
She said: "I`m not a narcissist! OK, I`m a narcissist, but that would be over the line.
"Having sex to your own song, that`s horrible. I`m a good Christian girl."
The raunchy conversation continued withKaty questioned on whether she has ever had a threesome but the star would only say "no comment".
Despite her jokes, Katy has previously confirmed she will collaborate on a song withRihanna but wants to make sure it is "iconic".
She said: "It`s one of those things that`s got so much build up that we have to deliver...I definitely want to do something that is so iconic.
"We`re both busy but we planted the seed two years ago. How disappointed would you be if that song came out and it`s no good?"