It's rude to make derogatory comments about someone else's food.
Dan is sitting next to James in the school cafeteria.
Dan wants to socialize during his lunch break.
Dan tells James that his sandwich looks interesting and asks what's in it.
Dan tells James that the sandwich he is eating looks disgusting.
James tells Dan how he made his sandwich, and they talk about different foods they like.
James is annoyed by Dan's insult and gets up to move to another table.