A week after finishing my first marathon, I've decided what the worst part is about a marathon: not being able to wear your medal for days at a time as you go out and do errands, go to work, have a beer, etc. People really look at you when you do that.
It just seems wrong that you really only wear it around the finish line and back to your hotel, and maybe to the airport (but they make you take it off to go through security). My theory is that we should a grace period of a week for a half-marathon or marathon (anything that is medal-worthy, really) and we should be fine wearing it around. So there you go: it's now a new rule.
Oh, and the second worst thing about a marathon, thanks to CewTwo: