When I first encountered the Hong Kong Island district of Happy Valley, or Faai Wuht Guk in Cantonese (快活谷), I knew the name originated with the British, but not how it was chosen.
Prior to the colony's birth the place was anything but happy; the British Army had to shut down a camp it had established there in early 1840 to prevent more soldiers from dropping dead of malaria and other mysterious fevers. The valley, filled with marshes and rice paddies fed by a river that indigenous people called Wong Naih Chung (黃泥涌), or "yellow mud river", was a breeding ground for swamp-related diseases.
Thus when William Brodie, a British naval officer aboard the HMS Rattlesnake (in Hong Kong after participating in the First Opium War in 1839), died in 1841 and became the first person buried in the new Hong Kong Cemetery, a brief journal notation by the ship's doctor Edward Cree on June 18 gave the valley its name:
Soon afterwards he became comatose and the fine old sailor and good-hearted man breathed his last. Poor old Brodie was buried in the afternoon in the new cemetery in 'Happy Valley'.
At the time "happy valley" was a euphemism for a graveyard.
Later, after the British drained the paddies to construct Hong Kong's first racecourse in 1846, the Chinese nicknamed Happy Valley Paau Mah Dei (跑馬地), literally "race horse place", and the origin of the name was forgotten. Over time Happy Valley became synonymous with horse racing, which in a way makes perfect sense: the happiest people there are those who win big.
To superstitious Chinese folks, equating the name with a windfall is a far more appealing concept than thinking about the boneyard.