A guy at my church had a real carbuncle in the middle of his back. He'd been having pain and let his wife look at the place, but she said it was just a red bump.
He left it alone, but it kept getting worse. Finally, his wife saw it and told him he needed to go to the ER. She showed it to him in the mirror and he said it looked awful.
He went to the ER and the doctor had everything laid out to lance a boil there in the department. Then he looked at the place on my friend's back and freaked out. He said it needed surgery as soon as the doctor could get there, and he admitted my friend right away and they took him to get him prepped for surgery.
The surgeon said it was a good thing he got the carbuncle when he did because my friend was well on his way to having a bloodstream infection. He had a crater in the middle of his back where the carbuncle was. It was pretty scary.