Staying with the armpit theme from last week, here is a trick I learned a couple of years ago. Now that I am married, this trick comes in especially handy;)
It is a super simple and easy trick that relies on ... yep, you guessed it, white vinegar. All I do before I wash shirts is squirt the underarms of the shirts with white vinegar. Then I wash them like normal in the washing machine and voila, no more sweat smell left on the shirt.