[ Luffy is a lot of things, but he's not a liar and he tries to keep his word, even if it's something outrageous like...fighting the Four Emperors. But he's especially serious about food. So he buys a full size honey for himself and one for Eren and he figures that will make them even. Does he know or care how much these things cost? No. But it's probably not enough to get Nami on his case. ]

A thief? No. I'm a pirate.

[ It might seem like a semantic difference, but it's a huge difference to Luffy. ]

We fight people and have cool adventures and stuff! We aren't really thieves unless we gotta be.

[ Except for Nami, maybe, but he's not going to drag her. ]