T-shirts aren’t just a business, they’re a religion. In the U.S. alone, $20 billion worth of T-shirts are sold annually, according to NPD Group. That whopping figure includes repeat customers who just can’t get enough. In fact, the average American owns about 15 tees and they’re the number one clothing item purchased by men in the U.S. With numbers like these, it’s high time we all brush up on the basics. For 10 easy ways on how to wear a T-shirt no matter the occasion, click on the gallery above. Now, who’s ready to tee off?