I can still remember the first commercial I saw for Underoos, during the Plastic Man cartoon, your underwear could make you Superman, Darth Vader and even the Dukes of Hazzard! I was sold but never saw them in stores growing up (My mum was a "Marks and Sparks" shopper).
As an adult a friend gave me a Shazam! set as a joke. I seem to recall a very tall and thin friend trying the shirt on at a party. My son wears that Shazam shirt to this day.