Letting loose! John Mellencamp stopped by the Late Show on Monday, April 27, and had a hilariously off-the-cuff interview with host David Letterman.

The "Jack & Diane" singer, 63, smoked throughout the entirety of his chat with the longtime TV personality, 68, and acknowledged his poor health and continued bad habits as he spoke. 

Mellencamp took the interview to a surprising place when Letterman asked him the simple question of how he spends his days.

"I have a routine, you know," the singer began. "I work out, and that was really fun, cause we both had heart attacks, Dave, you remember that part?"

Letterman did undergo heart surgery in 2000, while Mellencamp's own scare took place in 1994. "Your heart attack was in Japan for god's sake, wasn't it?" Letterman questioned. 

"No... Letterman's always got everything wrong..." Mellencamp said slowly, struggling to remember the correct location of his attack. "It was in uh... uh... New York." 

When the funnyman asked the singer whether the heart attack took place while he was performing, Mellencamp had a tough time recalling once again. "I don't know! You can laugh but you don't know when you have those things!" 

"I didn't feel well, I was on tour, and I went back to Bloomington, where they have real doctors," the Indiana native continued. "The guy looked at me and he said, 'You've had a heart attack.' I went nuts... I called him everything in the book... He said, 'John, you can say whatever you want to me or act any way you want, but a first-year medical student can tell you you've had a heart attack.'"

"They'd been telling me for years to get on cholesterol medicine and I would go, 'Am I alright now?' And they'd go, 'Yeah.' And so, I'd think, 'Well I'm alright now...'" added the star. "But if I would've done what they had told me to do in the first place... My arms hurt, both arms hurt, and I was more grouchy than normal. I was more bitchy than normal."

The attack was not enough to scare Mellencamp straight, as he took continuous drags on a cigarette as he spoke to Letterman. 

"Here's the way it plays out, Dave," he began of his smoking habits. "I'm only good at about three or four things and smoking is my strong suit. My body is so polluted that anything — now, I'm not a doctor, you know that, right? I'm not a doctor — So I figure, my body is so polluted now that nothing can live in there. Cancer can go in there and go, 'I'm not going in there!' There's gotta be somebody else better to go into and destroy." 

"I'm gonna keep smoking and I'm good at it," he added. "I've written a couple of good songs, I'm kind of good on stage, and I have a good first kiss. Other than that, I'm not worth a s--t. I'm useless!"