your post just brought back SO many memories. my dad had a restaurant for 10 years. can’t say how many times he would have customers buy a full meal, then at the end say x was too hot, y was too spicy etc. and then expect not to pay/refund/coupon… if you don’t like the food, STOP EATING! if you eat the meal then complain, you’re a shnurrer plain and simple. and just FYI, the managers/proprietors/waiters all know what you did.
sorry. don’t know the halacha though.