There are certain things, as a customer in a restaurant, that you're not obligated to respond to. It's polite, for instance, to respond to your server's polite smile as he/she walks by to check on you. But you don't have to respond. If you see your server's eye twitch when you order something, you don't have to ask about it--although you probably should.
Other things, however, you need to respond to. Nonverbal things that require a response are things like your server stopping at the table. Shut the fuck up and answer my question, okay? You can continue bitching about your neighbor in a second.
The appropriate respond when your server speaks to you? A goddamn answer. I had these two women last night, one of my last tables. I delivered their food and asked if they would like anything else. One told me she'd like another beer in a few minute--hers was still half full. I smiled and said okay, anything else when I come back with that? Nope.
So I sat down and had a couple bites of my dinner, then rang in her beer when I saw from across the restaurant that it was getting low. When I got back to the table, maybe four minutes had elapsed.
"How is everything?" I asked as I set her beer down. I could see they hadn't eaten much, if at all, but they'd been talking to I assumed that was why.
"Well," said one of them, starting with the attitude. "We don't know, do we! We need some ranch, two sides of ranch, and two plates, and we need water!"
I blinked at her, said I'd be right back, and muttered under my breath the entire way to the kitchen: "Maybe you should've fucking spoken up when I asked you twice if you wanted anything else, bitch. Who the fuck sits there not eating because they don't have enough ranch, they already had some, Miss Thing should watch her fucking attitude or they can have two sides of my foot up their ass." Yeah, I get pissy when little just-turned-21 girls get snotty with me.
They didn't use the plates. They didn't use the extra ranch, only the one that was on their goddamn plates to begin with. And only one of them drank any water. Am I surprised? Ha!