This smoggy, humid city was named the planet's hottest city by the World Meteorological Organisation. Bangkok has an average annual temperature of about 82 degrees Fahrenheit. The possible exception is late December and early January.
Although temperatures soar much higher elsewhere in the world, Bangkok makes our list for the simple fact that its hot here for so long and there's little respite. Even at night, temperatures barely drop so the heat is unrelenting. As the Telegraph notes, Bangkok is "rather uncomfortable all year round."