Extra: 3 days later, as the Strawhats and Law are on their way to Dressrosa
A shadow crosses Law's face as he observes the bandages on Luffy's right wrist. Certainly he had seen some strange things the past few days, and he had come to realize what a crazy, unpredictable man he had made an alliance with. But he had never once equated the words "attempted suicide" with Mugiwara-ya. He stared at the bandage, long enough that Mugiwara-ya noticed.
"Ah this? It's kind of a pain, but Chopper won't let me remove it yet."
"So the tanuki knows about it as well."
"Shishishi, yep!"
If Law was the kind of person who made conversation, he would have asked if there was anything Luffy wanted to get off his chest. If Law was the sentimental type, he would have given the boy a quick hug. But he is neither of the two. So he can only sit in silence and say nothing. To each his own pain, I suppose. And it was apparent from that brief time on Amazon Lily that Mugiwara-ya had enough pain to deal with.
"Oy, oy, Luffy, you're making a big misunderstanding again!" Usopp hangs an arm over Luffy's shoulders.
"Am I?" Luffy makes an innocent, doe-eyed expression.
(one explanation later)
Law sits still for a moment, his face obscured. Then he karate chops Luffy's face, saying, "Then say that kind of thing from that start!" and gasps.
Staying with the Straw Hats was making him go out of character.
Note: In case you were wondering what kind of face Law was making, it's the "I hate bread" face from episode 629. Look it up :3