-Not showing cuff in a blazer/suit. It's more of a pet peeve, but I've seen many outfits there are otherwise great, except for this detail. I prefer a healthy amount of cuff, though, and I believe that it should be showing at *all* times.
-Hideous running shoes. Appropriate when you're actually running, or doing some sort of physical activity.
Amen brotha. All my friends wear horrifying basketball/running shoes constantly and the quickest way to show you have no idea how to wear a suit is to be not showing any cuff (hello to half the people who ever participated in a wedding).