So basically here's the deal: I'll call him Adam. We have been friends for something like eight years. Adam really really really likes to talk. He can't stand silence. I have always been sort of uneasy with him necause he's pretty dorky and he's really dramatic and gets annoying. But the problem is we both run cross country for our school. Since I am one of his only friends he would always stick with me, and since I was interested in philosophy and politics and religion and that sort of thing, we would have long deep conversations about that. Now, for reasons I'm not going to explain, the prospect of talking about that makes me want to die. How can I tell a person who approaches me saying, "What should we talk about today" that I want to run alone, in silence?

How about saying, "I want to run alone, in silence today. Sorry."