There's an interesting parallel between Luffy's second visit to Amazon Lily and his first. When he wakes up after the war Luffy very understandably is quite self-destructive. There's a part of him that's in denial even as he realizes that his brother is dead
It was much the same way after Sabaody. Luffy never thought his crew was dead, but he was reckless to the point of self-harm even as he berated himself for not being strong enough to save his friends. The post-Sabaody chapters are much more humorous, with Luffy getting high on laughing mushrooms and being on the receiving end of an accidental hand job, but Oda set up a pattern of behavior for how Luffy deals with loss and grief.
This is something Oda does quite frequently--he sets up a character trait or problem in a way that initially is very funny, only to pull the rug out from under the reader and play it for serious later on.
