Scout was saying he was habitually mean. He didn't equate being a dick with being mean necessarily. He was mean often, but he was a dick almost all the time. He interpreted the word more along the lines of he liked to fuck with people and wasn't polite. He was also confrontational. And he had no problem with that. He preferred bluntness to the faux-kindness everyone else seemed to ooze. Gross.
"Well, thanks," he said off-handedly, looking at the sword again. He studied its weird little ornamental swirls on the hilt that he was sure had some sort of hilarious scientific/artistic name. After a moment, he turned his eyes to the girl again. "Then consider me rooting for you."