So far I haven't had too many horrible disasters.

Got bumped on a family trip when I was a kid. I didn't care too much, but mom was in a sobbing panic.

Lined up a last minute cheap hotel room somewhere in Slovakia without checking into the details deeply enough. It wasn't a hotel just an old apartment building with an abandoned restaurant on the first floor. I'd missed the "must call well before arrival" so there I was, standing in front of what appeared to be an abandoned Soviet era block, at dusk, in a neighborhood that was looking ever more sketchy.
I have no idea how they managed the photos that were on the listing. Spent some time on the phone with hotels.com, until they sent me a credit code for the amount via email. Sadly, I was never able to use the credit. By the time I tried, I was no longer in Europe, and it was apparently only good for Euro listings.

Current debacle: Cross-country / circumcontinental trip in a camper van. Mid-Saturday, alternator craps out. Currently in nothing-open-on-Sunday limbo. Bah.