A shirt is an article of clothing. Haha. Get it? Cuz this is an article, and it's about clothing, so it's of clothing. Ha. Okay moving on.
Shirts are known for only being worn by people. However, people like to sometimes torture their pets and make them wear "cat clothes" or "dog clothes" to make them "look better". This method does not always work, however, due to the fact that sometimes clothes do not fit dogs or cats. But now, people are even putting clothes on birds now, which, of course, gives them cancer, unbeknownst to the host (the bird) of course. Though.
Shirts have been worn ever since the 1990's.