It is interesting that someone besides Hawkins can make predictions about the future. It certainly changes the discussion about whether or not fortune-telling was related to his Ability. But enough about that, on to the over-analysis of Luffy's speech patterns!
"Do you poop?" - A vulgar question to be sure, but with a surprising hidden meaning: Only a real, living creature can poop. Luffy is a dreamer at heart, but his simplicity mires him in a world of pragmatic answers. To someone like Nami, Reverse Mountain was an incredible phenomenon, stretching the laws of physics while at the same time reinforcing them. To Luffy, it was just a "Mystery Mountain". But he truly wants to live in a world where living skeletons and mermaids aren't just figments of his imagination. And just imagine his dismay if he were to ask "Are you real?" only to be told "No." The poop question, even if answered in the negative, is a much easier let-down.
"Don't take meat lightly!"- For someone that regretted befriending the beasts of the jungle simply because he missed out on eating them, this phrase shows a remarkable degree of respect for living things. Meat doesn't grow on trees- although there are experiments underway, I'm told. Meat is processed from the bodies of animals. In order for there to be meat to consume, a living creature must die. I'm no vegetarian, but I try not to take meat lightly.