I don't want to pay for a meal.
That wouldn't be good. Why don't you want to pay for it?
It was too expensive.
I hope you enjoyed your meal, but it is wrong for you not to pay for something you ordered. You should have thought about the price when you placed your order.
They were treating so I don't have to pay.
Even if they were treating you shouldn't have ordered something so expensive. It is not nice to order something expensive when you don't pay your share.