In order to wear a vest with jeans you would also have to not wear a belt and have the bottom of the vest cover the waistband of your jeans. Doing this properly your jeans would have to sit on your natural waist. This means that the waistband would not have belt loops, but side tabs and buttons for braces. So, you would be left with wearing a vest, with braces and jeans up to your naval. You would be a walking contradiction of formal and casual.
Now, would you honestly wear that?