I'm guilty of the "it's only a short trip" excuse, though even then the absolute minimum I wear is a full face helmet and armored jacket. On any sort of ride, I suit up. Field Armor boots, knee/shin pads, vest, and shorts. Joe Rocket Phoenix4 jacket. Icon sheepskin gloves, and Icon Alliance SSR full face helmet.
People rag on me all the time about how much gear I wear and how "I'm gonna roast" as soon as we stop. Even with all that gear on, I'm really not all that hot. Sitting in traffic on a hot day with the rad fan blowing, I get a little warm, but honestly it's very bearable, and as soon as I start moving I'm totally fine again. Most of the people I ride with own jackets, but the air temperature determines whether they wear it or not. So they ride with a beanie-type "helmet", t-shirt, jeans, and sneakers.
I really like Icon's "field armor" line.....good prices, and in my experience it's quality stuff. I've been wearing the boots and kevlar leg armor for 2 seasons now and no issues at all. It only has to work once to be worth it's weight in gold.