KATY PERRY is about to go all TAYLOR SWIFT on her ex-boyfriend, JOHN MAYER . . . meaning, she's going to write a song about him. Ironically, John has been in this position before . . . with Taylor.
Katy tells "Cosmopolitan" magazine, "There's no bad blood. But I'm sure there will be inspired songs."
John doesn't seem to mind though. He told the paparazzi, "I have super strength for gang-ups. I'm fine. That's what you're supposed to do, man. You're supposed to write songs. You're just not supposed to tell everybody you're doing it."
Although that sure sounds like a dis . . . if even a minor one.
Speaking of Katy and her exes, she has supposedly reunited with one of them. The British tabloids claim she was seen "kissing, flirting, and cuddling away" with FLORENCE AND THE MACHINE guitarist ROB ACKROYD.
They spent some time together back in 2012.