It's in an interview
Q: Haruhi hates boredom most of all and seeks "extraordinariness" in school life. And the one who is always at her beck and call is the narrator of this story, Kyon. He is an ordinary boy with no outstanding features, whose name is not even revealed. What do you think about him?
Nagaru: Though I could give him a decent name, I thought it feels stupid and funny that he is called by that queer nickname from beginning to end. As for his featurelessness, I originally planned he would be an esper, but while writing the Prologue, I had subconsciously turned him into a common person. And you said he is an ordinary boy, but I think, in a sense, he is not an ordinary boy, such as his way of thinking.