Jace shook his blond head in exasperation. "You had to make a crazy jail friend, didn't you? You couldn't just count ceiling tiles or tame a pet mouse like normal prisoners do?

”

Jace is showing his frustration to his friend who has made a friend in jail. Jace believes that making a “crazy” friend in jail is not normal and doesn’t understand why his friend has done that, instead of doing something that is more common, such as counting the tiles of the ceiling or getting a pet mouse.