The man, who is currently unidentified, walked in on his girlfriend having sex with someone else. He proceeded to knock the strange man unconscious. (Which is already more than you are allowed to do by law when you catch another man sleeping with your girlfriend.) (Legally, all you are allowed to do is nothing. You are allowed to do nothing.)
But according to the Chicago Tribune, that wasn't enough:
“This will be a lesson to you, I lit your (genitals) on fire,” he told the 30-year-old while using a Bic lighter to burn the man while he was unconscious, according to a police report.
The man ran to a laundromat at 44th Street and Ashland Avenue, where police found him applying Vaseline to the burned area in an attempt to sooth the pain, according to the police report.
First off, the lion's share of blame does not reside with this stranger having sex with a woman. He may have even thought she was single. What this man should have done was ask the stranger to leave, then had a calm, rational discussion with his girlfriend about what his definition of monogamy is. Not burn the guy's balls off. No one, under any circumstances, deserves to have fire held to their dick while they are unconcious. That's just common decency.