RE: WTF did you fidots give it away to begin with?
It was originally Chinese territory that the British forcibly told China to lease to them after the opium war (under the last Dynasty of China, the Qing Dynasty ). China leased HK to the British for 99-years in 1898. The UK was simply keeping her end of the agreement.
If I remember correctly, part of the territory of Hong Kong was leased for 99 years and the other part was British with no time limit, but the British made both parts subject to the 1997 agreement.