Like the denim vest.
First of all, I hate vests in general. If you need an extra layer, wear a sweater or a full-on jacket. The problem is that people who wear vests are simply doing so because they feel it is a wonderfully fabulous addition to their outfit. FYI: It isn't.
Adding the denim factor makes it a whole other disaster. Denim on top is difficult to begin with. You can't really wear it with jeans because then you either look like you're wearing a denim suit, or the denim just doesn't work with the other denim hues you've got. And it doesn't quite look right with much else either (there are a few exceptions, of course).
The vest combined with the denim makes a hideous hybrid of fashion disgust.
It doesn't help matters at all if the vest is bejeweled, studded or "artfully" ripped.
Let's stick to flattering clothing that has a purpose, k?