He had a fight with his girlfriend outside a restaurant and said he was going to teach her a lesson.
So he began repeatedly banging HIS head against the concrete sidewalk until he was covered with blood. At some point police and paramedics pulled up, and to continue proving his point, he began banging his head repeatedly on the police car's windshield until it shattered.
He then went back to smashing his head on the sidewalk, which continued until he got tasered, and then needed Valium.
The admitting diagnosis was "Self assault"
Exactly what lesson his girlfriend learned from this is unclear, but I suspect it had something to do with getting another boyfriend.