Why do wet clothes dry slower on a humid day?
When clothes or other wet items dry that are losing their moisture. That moisture has to go somewhere. In the case of drying clothes the moisture evaporates into the air. The molecules of air that touch the clothes make bonds with the molecules of water. The air then lifts the water away tiny piece by piece.
The warmer the air the faster it moves and the further apart the molecules are allowing for more space to fit things like water. So when it rains on a hot day the air picks up a lot of the water making it humid. When you have wet clothes on a humid day there isn’t enough room in the air for the water in your clothes to move into, there is enough room somewhere but the spaces are harder to come by. So because there are fewer spaces for the water to move into your clothes dry slower.
Hot days are of course better for drying clothes in general, but if it recently rained then your clothes will be competing with all the rain water for spots in the air.
Sometimes there is so much moisture in the air that the water will condensate on cool things, like the side of a pop can.