You were walking around and weren't paying attention to where you were going.

"Ahh!~ I'm hungry..." Luffy groans as he rubs his stomach with a frown, looking around frantically for someplace to eat.

Then you bump into each other on accident, you fall to the floor with a yelp, and he just stumbles back.

"Ow!" He yells, looking down at you. "Hmm...hello!! My bad, let me help you up!" He grinned, holding a hand out to you.