Hot, high-humidity days are the days I like to go out and run several miles. A lot depends on your fitness level. And Westerners are becoming decreasingly fit.
Btw before you write angry replies accusing me of not knowing what I'm talking about I grew up in a part of Asia that gets extremely warm/humid in spring and summer. We're talking way above 80% average humidity for over 4 months, some days close to 100% and subtropical temperatures around 30-35 and above 40°C when it gets really hot.