Green Day frontman calls Psy 'the herpes of music,' Psy responds

Green Day frontman Billie Joe Armstrong returned to the music business in March after undergoing successful rehab.

So far, Armstrong has flown under the radar and things with Green Day seem to be back to normal.

But Armstrong, 41, has some things to say about K-pop sensation Psy. And he let everybody know about it on his Instagram account in a caption on a photo of Psy.

Armstrong wrote, "The dude is the herpes of music. Once you think it's gone, it comes back." He followed that with three hashtags: #herpes, #flareup and #pleasegoaway.

Psy took it as a compliment, he said in an interview with Fuse.

"I kind of like it, it's cool," he said. "He said I'm like the herpes... that keeps coming back. I think it's really cool. Thank you."

This revives Armstrong's barrage of top-40 hate, including a diatribe about Justin Bieber at a Las Vegas show. The rant led him to check himself into rehab and postpone Green Day's tour.

Looks like Armstrong will have to pick on someone else.