An amazing contribution from the Style Forum member Bourbonbasted:
“I’ve said this before, but I’ll go on record again. Sport Coats, or blazers, can work with jeans. However, the inherently casual nature of denim demands an equally relaxed SC. This means natural shoulders, patch pockets, a more casual drape, a more rumpled material, etc.
You also need jeans that fit properly. Skin tight and a SC will never work, just like dad jeans make for a no-go. The rest of the fit needs to be casual, too: loafers or chukkas, a rumpled shirt (or OCBD) and a playful tie (if you must, though I wouldn’t).
90% of the jacket/jeans combos I see are failures because a dude tries to pair a worsted jacket (or worse, a separate) with structured shoulders and flap pockets with a pair of dark denim that is a size too small. This will always be fail. Always.
Just as we see unbelievable fails in CM casual (a thread at the Style Forum), jeans with a SC is not simply tossing jeans on after you get home from the office. It’s a completely separate look that demands a totally different thought process.
The photo (above) supports my point”.