He refused to sit on the chair that he made because the
chairs were made of the hair of the king of Brobdingnag. In the 7th
chapter, the King had shaved his hair and Gulliver had weaved the hair into
chairs just to satisfy the Queen of Brobdingnag’s curiosity.
The reason why Gulliver refuses to sit on the chair he has made for the Queen of Brobdingnag is because the chair was made from the queen's hair; therefore, sitting on it, according to Gulliver, would have been insulting to her. In other words, Gulliver believes that sitting on the queen's chair would not be an honorable thing to do. This is part of Chapter VI (Part II) of <em>Gulliver's Travels </em>written by Jonathan Swift<em>. </em>