Being packed into the resort buses like sardines, standing, after 14 hours in MK. Totally the pits, and my least favorite thing about WDW, worse even than leaving. HATE the buses, and whenever it's remotely affordable, we rent a car.
Of course, worse than the buses was the time I got food poisoning at 1900 Park Fare. It was the night before our last park day, it was just DD (7 at the time) and I left from the group we'd traveled with, and we were looking forward to a Mommy/Daughter day at MK for our last day of vacation. Didn't happen. In fact, I was lucky I could make it to MCO and tolerate the flights next day. That really WAS the worst
but fortunately a "once in a lifetime" experience!