I left one of my Jool mission ships in orbit. Somehow, it had gotten into a retrograde orbit (probably because I wasn't paying attention to the transfer too much) of 100km x ~1000 km. My largest station at the time orbited at 125km prograde. I was docking the second of two of my service crafts, a practice I adopted both from experience and from copying some real-world protocol of always having a way for the crew to get home. When it was about 50m out from the station, the interplanetary roars in at a wild speed and clips the solar array and fuel tank sections of the station, destroying them and throwing the whole station into a fairly fast spin. It hit the service ship and knocked it away about 400m before I got the spin under control enough to zero out my relative velocity. In the impact, the ship's docking port and parachute were destroyed. I had to launch two rescue missions to get all the Kerbals before deorbiting my now-useless and horribly unbalanced station. I was sad that day. I haven't left a ship in orbit when I'm done with it since.