Don’t phunk with Katy’s heart.

The “I Kissed A Girl” hitmaker is making headlines after publicly bad-mouthing her ex-boyfriend Travis McCoy during a recent performance at the Wiltern Theatre in Los Angeles.

“Girls, if you have ever dated a boy — specifically the lead singer from Gym Class Heroes — don’t do it! Boys should have a heart. You know what I mean girls? Boys just want the milk, but they don’t want to buy the cow.”

The 24-year-old’s jibe comes is response to Travis’ own verbal assault on his blog, on which he wrote: “We fight every night, now that’s not kosher. I reminisce with bliss of when we was closer. And wake up to be greeted by an argument again, You act like you’re 10.”

Travis and Katy ended their two year romance in December.