Once, in COS, we boarded a DC-10 from the right side. And yes, it was a UA DC-10 in Colorado Springs! We circled Denver for 2 hours waiting for a storm to pass, and had to divert to COS for fuel. Some passengers wanted off (their destination was COS) so the plane had to go to the terminal. Many (including me) got off to walk around, and re-boarded on the right. It was so unusual that I still remember it.