Why is Arthur Dent considered boring in The Hitchhiker's Guide to the Galaxy?
Arthur thinks that his friends feel he is boring.
Arthur Dent is considered boring because he is just an ordinary guy who is "never quite at ease with himself."
He worked in local radio which he always used to tell his friends was a lot more interesting than they probably thought. (ch 1)
Arthur is just an ordinary guy, until he drinks special beer and goes traveling through space to save Earth. As thirty-year old radio worker there is not much about Arthur that is special. Why Arthur thinks he is interesting we do not know. He did try to lay in front of the bulldozer to save his house (although the house was not important to anyone but him, and was only important to him because he had lived in it for three years). Most of the aliens also consider Arthur boring, calling him "Monkey Man."