NEW YORK - Popular Korean rapper Psy said "it's cool" that he is called the "herpes of music".That unkind epithet came from outspoken Green Day frontman Billie Joe Armstrong, who wrote on Instagram on Wednesday: "This dude is the herpes of music. Once you think it's gone, it comes back," reports The Straits Times. He posted a photograph of Psy and added the hashtags: #herpes, #flarup and #pleasegoaway, New Musical Express reported.His comment came after the release last month of Gentleman, Psy's follow-up video to his Gangnam Style hit.His diatribe reportedly drew more than 20,000 "likes" from Instagram users, and nearly 2,000 remarks from fans mostly agreeing with his description.Interviewed by New York's Fuse TV, Psy reacted: "I kinda like it, it's cool. He said I'm like the herpes... that keeps coming back. I think it's really cool. Thank you."The interview was posted yesterday. Psy, 35, is in the United States promoting Gentleman.Armstrong, 41, returned on the road in March after rehabilitation for alcohol and prescription drug abuse. His guitar-smashing meltdown last September forced his band to postpone a tour.