From The Absolutely True Diary of a Part-Time Indian:

“But you should approach each book — you should approach life — with the real possibility that you might get a metaphorical boner at any point.”
“A metaphorical boner!” I shouted. “What the heck is a metaphorical boner?”
Gordy laughed.
“When I say boner, I really mean joy,” he said.
“Then why don’t you say joy? You didn’t have to say boner. Whenever I think about boners, I get confused.”
“Boner is funnier. And more joyful.”