Back when I first met my husband he sent me a story that he wrote using only dialogue, which inspired me to write one of my own. This is what I came up with:

Thinking too Much  
by Grace R. Pringle 

“What have you been doing?”

“You, what have you been doing.”
“Yeah, YOU.”
“I’ve been thinking.”
“For the past hour? The whole time? What in the world could be so important to think about so much?”
“That’s the thing, there is nothing important anymore. I was thinking about how there should be more important things to think about.”
“What are you talking about? There are plenty of important things.”
“For YOU maybe, not for me.”
“Come on, there must be something, at one time or another, which you thought was important.”
“Sure, but that was before, I’m talking about now, what’s important now.”
“That’s easy, it’s all still important, just because time has passed doesn’t mean the importance of important things has changed.”
“That’s because you think important things are important, see, I just think unimportant things should be important because they aren’t.”
“Alright, fine. As long as you still acknowledge that there are important things to think about.”
“Do you think thinking is important?”
“Of course, why wouldn’t it be?”
“I dunno, it just seems that there are other, more important things to think about instead of thinking.”
“I think that all depends on what degree of importance thinking is on.”
“But if something is important (whether or not it is very important or just slightly important) isn’t it all still important and should be treated as important even if the other thing is more important?”
“You stopped.”
“Stopped what?”
“The flow of conversation. We were talking and then you said ‘yeah’ and you stopped.”
“I couldn’t think of anything else to say, you were going in circles. At least… I think you were.”
“Why didn’t you just say; ‘you’re going in circles” then?”
“I thought it would be rude.”
“Then you should have said “I don’t mean to be rude (or do mean to be) but either way, you’re going in circles.’”
“That would be your statement, not mine.”
“Well, it would have been yours if you had said it first.”
“I would not have thought of it because it was meant to be your thought, not mine.”
“How do you know it was meant to be mine if you had said it first?”
“That’s stupid, there isn’t such thing as “what could have been” it happens the way it happens or is thought the way it is thought and there are no exceptions because there was no other way to go about it even if there appears to have been.”
“That’s what you think, it isn’t what I think.”
“Doesn’t one of us have to be right? I don’t think there can be two rights about a one, don’t you?”
“I have not thought about it. Mostly because I wasn’t sure if thinking was important enough to think about thinking it.”
“Let’s just say it is all true and leave it at that.”
“But it has to be solved; if we say there are two rights but each of us is convinced there is only ‘one’ doesn’t that create a paradox and collapse time and space and thought and all that is important about there being “one right?”
“I don’t know… maybe we should think about it.”
“I was before you asked me what I was doing.”
“… And you only spent an hour thinking about it?”