This writer has recently become aware of some confusion among friends regarding different types of men's shirts. Some have queried, "What is a dress shirt?" Others have asked, "Isn't a polo shirt a sport shirt?" or "Is a sweatshirt a sport shirt?" Still others have asked, "When is lunch?"
Here's a brief overview that should clarify things for you. (TIP: You may wish to print and post it on your refrigerator for future reference.)
Men's dress shirts are very often white or blue in color or pattern and may have a button down or straight collar. Sometimes they are referred to as "button-up" shirts, because you "button them up" to wear them. Which means you can actually wear a "button down button-up" shirt.
Spoiler alert: If you don't find that observation amusing, you should probably stop reading now because it's all downhill from here.
Dress shirts are commonly worn by men like me who sit behind a desk all day complaining that no one understands how much we have to do, what pressure we're under, how cold (or hot) our office is, and wouldn't it be nice if someone would fetch us a cup of coffee about now?
A sport shirt usually buttons up the front and often "sports" a pattern so loud it's difficult to hear what the wearer is saying. A "Hawaiian" shirt can be a sport shirt; so can a "camp shirt," although in most cases the wearer is neither in Hawaii nor at a camp, but sitting at the desk next to yours loudly eating an onion and sardine sandwich with mustard on rye while checking his Facebook page again to see how many "likes" the picture he posted this morning of his cat in the bathroom sink is getting. (18 "likes," 1 comment, but no shares yet.)
Often short-sleeved, this style of shirt is most popular with men who need to wear a "collared shirt" to get into a restaurant, but who do not want to wear a "dress shirt."
A men's polo shirt pulls over the wearer's head like a men's T-shirt, but has a collar. It is usually worn to play tennis, not polo, hence the name. Similarly, a sweatshirt is worn to repaint the dining room walls for the third time this weekend because your wife can't find the exact shade of eggshell she was looking for – even though you were planning to watch football, a sport in which the players wear shirts called "jerseys," named after a type of cow and a place in England where most men wear rugby shirts. (I may have made that up.)
In conclusion, no one knows what a shirt-jac is or why you should wear one.