Johnny C held up a train in Gotham with a bomb strapped to himself. He ranted to the passengers that the city was awful and diseased and that maybe by blowing up the train he could get people to take the hint and leave. He referred to himself in third person a lot as well.
Stephanie was dragged along the a train as she rushes to dispatch. She managed to get in the train after Oracle killed the lights, busting through the window and kicking him in the face with a shouted "peekaboo". Johnny attempted to punch her while saying he apologized in advance for messing up her beautiful face, but Steph easily dodged him, saying "Careful, you'll make a girl blush."
Johnny restated his name once again, and Steph grabbed his trigger from him, making sure to keep her thumb on the button so the bomb didn't detonate, sweetly asking if he didn't mind if she borrowed it. The confused Johnny shouted "No. What? Wait! Yes!" But Steph kneed him in the stomach, saying "No takebacks." As the citizens in the train applauded Steph's takedown, the stunned Johnny muttered that she was beautiful.
In fact, Johnny remained so infatuated he even shouted "Johnny C love you!" to Steph as the police took him away!
All this happened in Batgirl #9.
The end of Batgirl (third series) (12) showed C's infatuation remained even from his jail cell. He read about her exploits taking down the Blimpmaster, his cell mate noting he was obsessed. He said Batgirl was amazing, he couldn't wait to see her again, and most ominously, that she was going to need all the help she could get. He was surrounded by cartoon drawings of unrecognizable superheroes, their true purpose unknown.
Johnny C returns in Batgirl (third series) (15) when Steph is trying to protect Newton, the geeky, science guy she goes to school with. He appears in a strange costume, calling himself the “Grey Ghost”, and claiming to be there to “help” Batgirl out (though it seems like he is really just stalking her). Oracle does a voiceprint on him and discovers that it is in fact Johnny C, or Clancy Johnson, the same guy Steph stopped from bombing a train (he was released from prison due to mental instability). He disappears in a flash of bright light, telling Steph that they will meet again.