That happened to a guy I know. Actually, I don't know if he was packing at the time, but he was unconcious, and the medics were going to have to catheterize him. Fortunately, he was carrying a card that listed a good friend, who was also FtM and who was involved in training medical personnel in how to deal with trans patients, as his emergency contact.
As soon as this friend heard the word "catheter" he called out, "Stop!" He then quickly explained that, although they were expecting to catheterize the patient like a male, they would need to do it like a female. "O.K. Now, GO!"
The story is kind of funny the way he tells it, but I'm sure it was stressful at the time. It also goes to show how important it is to have up-to-date emergency contacts on you at all times, and that you should carefully consider whom you choose as your contact.