The conversation between Gin and Tousen in Chapter 1.
"I remember what he said. Help me up. And please stop smiling."
"You're blind. You can't see me smiling."
"Gin, you're always smiling."
- [Gin] grinned wider. He did like to smile. Maybe it was his default facial expression. For some reason it threw people off guard, which wasn't a problem at all. One time he squinted his eyes nearly shut and walked around for a day. He'd made people really uncomfortable with that, which was even better. Of course, Rangiku had taken one look at his squinty-eyed self and walloped him across the face. So that had been the end of that.