A lot of men these days are asking, "What's the difference between a blazer, a sport coat and a suit coat?"
Which reminds me of a joke: a duck walks into a bar wearing one shoe. The bartender says, "Hey, you lost a shoe." The duck says, "No, I found a shoe."
I love that joke. But I digress.
The obvious difference between a blazer for men, a sport coat and a suit coat is that most people don't know (and don't care) that there is a difference between them. Most people use the words as if they mean the same thing, which is like using "pants," "trousers" and "slacks" to describe the same item – when we were all brought up to know better, weren't we?
Historically, "blazer" described a solid color sport coat (originally only navy with brass buttons). If it was really nice-looking and a gentlemen was headed out for the evening, it could be said he "went out in a blazer glory." I may have made that up.
A sport coat (or sport jacket) was made from beefier fabrics, usually with a pattern, and was actually worn for sports like hunting and shooting. Time passed and hunters took to wearing a jaunty orange color while the sport jacket evolved into a garment that could be worn for casual events of any sort.
Suit coats were made of finer fabrics and had tailoring differences from sport coats because they were worn for formal events, not for shouldering a rifle or stuffing a dead bird into your pocket. Plus, they had matching trousers.
Then men – and I'm not pointing a finger at anyone in particular – started wearing suit coats as if they were sport coats: with men's jeans or men's chinos or other non-matching pants. And other men started wearing sweatshirts for men as if they were sport coats and they would go without socks and they thought that you could wear a t-shirt and shorts and flip flops to the office and that would be cool. Again, not pointing any fingers at anyone in particular [especially you, Ben].
And that's how the distinction between the three types of coats was lost to history. Frankly, I'm surprised anyone even remembers it, including me, because I have enough trouble remembering the joke I started out with.
However, you will enter the fray armed with knowledge: there are indeed distinctions between blazers, sport coats and suit coats.
And while no one else may care about them – just like no one seems to mind when people write "it's" when they mean "its" – at least you'll know the difference when you're playing trivia.