How can I stay positive during a hot and humid day?

It's okay to feel lousy when the weather stinks. This includes being unproductive. This also applies to family, friends, and coworkers, so do your best to give people some grace.

That having been said, here are a few things, in no particular order, that may help.

• hydrate. Drink more water than you think you may need. Drink even if you're already living in the bathroom. Seriously. You are losing more water than you may be aware of, so drink up. Soda and coffee are... okay. Water is a lot better. And please, no alcohol. It'll only make dehydration worse.
  
• Cold showers. If a truly cold shower is too uncomfortable for you, go for a colder finish, by turning down the hot water at the end. At minimum, make sure the following get cold water on them: feet and ankles, hands and wrists, scalp and the back of your neck.
  
• Go where the air conditioning is, if you can. Drive around if your car has a/c. Visit a café, and it's a bonus if you can work there, if they have a/c and won't kick you out. You may need to keep buying coffees. There are far worse ways to spend an afternoon.
  
• Buy a/c if you can afford it, but also afford to run it. Air conditioners can run as low as $200 or so for a basic model, but they also jack up your electric bill. Home a/c, on the other hand, will improve your quality of sleep, assuming you can afford it.
  
• If you can't afford a/c, fans are a decent next-best thing. Freeze a gallon jug of water, stick it in a shallow pan, and run the fan right behind it. Congratulations, you've just created a homemade swamp cooler.
  
• Don't cook unless it's the microwave. Don't do laundry or run a dishwasher unless you're desperate. Appliances give off lots of heat.
  
• Swap incandescent bulbs for fluorescent or energy saving bulbs. Lots of the energy that incandescents give off is in the form of heat

Hope this helps!