Luffy had been annoying Law for a bit, Law eventually got tired of this and looked at Luffy and put a finger in his face to shut him up, then Law takes two pieces of bread and puts it on both sides of Luffy's head still really annoyed

Law: WHAT ARE YOU!?

Luffy: Stares for a moment then starts to drool a little Delicious...

Meanwhile, you were sitting on the railing just watching and laughing your ass off