During his voyage to Brobdingnag, Gulliver had the opportunity to be presented to the King and Prince and the rest of the subjects. This happened after the Queen recognized him and brought him to the palace. As he got acquainted to his captors and began to make conversation with the Prince and King, he told him about his travels and some of the things that he has learned. He had also compared Brobdingnag to England in terms of how government treats its subjects, and he also spoke quite proudly about other topics such as the use of gunpowder, and the overall treatment of people.
Since Gulliver was tinier and much different than these group of people from Brobdingnag, he already was at a losing end: He represented every fear and bother that people feel about "intruders" or "aliens" that come speaking wonders about a place where they came from.
The King was not amused. He was shocked indeed, but the talks of Gulliver only made him confirm that England and the English were like vermin, and that they should not be allowed to walk the face of the Earth. Already the Prince disliked him for the very fact of seeing how Gulliver, tiny and all, would take so much pride of his native country, and so he resented him. The King, however, made it clear that England was not to be mentioned again, that their action were barbaric and that Britain, as a country, was not worth even thinking of.