what happens if you refuse to eat while on a flight?

Nothing - no one forces you to eat (there's never meal service on domestic flights anyway).

You do not eat.
You get hungry.
The Plane Lands
You get off.

Nothing. They're perfectly happy to let you go hungry.

They drag you to he galley, tie you down and MAKE you eat!!

Seriously - no one gives a d@mn if you eat or not. It is your choice.

Nothing. Nobody will force you to eat, except your mother.

Nothing. No one is going to force feed you.
No one will care either.

You can do that.

You might go hungry?

You miss a meal.

Nothing.

You will eventually get cobwebs around your bottom!

Seriously, nobody will worry about it, you will get hungry, but they won't refund the cost of the meal.

I'm sorry but I can't help you

i think all you have to do is politely decline the food

Your stomach ruptures