I can't really remember a horrible dining experience at a restaurant in terms of the food. I've been lucky. I've been to places where the service was terrible or non-existent, but not really any food I found inedible.
I have dined out with friends in various restaurants that were fantastic, very good and so-so.
But regardless of the food, there are a few times when the service was intrusive. When folks are just starting to eat, I think it a bit strange for the service person to inquire how everything is when I haven't halfway chewed my first forkful of food.
When a conversation is underway, is it really "good" service for the service person to constantly interrupt whoever is speaking to ask if one wishes more water or more wine? I appreciate a quiet refill on water. And a quiet, inquiring look as one holds a bottle of wine near one's glass is all that is required to get one's point across. The diner can either nod or hold his hand over the top of his glass. The speaker will not miss a beat and the "service" will have been perfection.
I've had a meal where the service person, apparently bored out of her mind, asked my party six times if everything was all right. It only took us 15 minutes to eat, so she asked, roughly, every two minutes.
Those are what I consider dining experiences from hell.