Well, there have been major speed bumps in our road of vacations, but never ruined.
In December 2000 my Mother fell down a small flight of stairs in MGM and blows out both her ankles. She spends the rest of the trip in a wheel chair, on heavy drugs (thank god!

).
January 2002 Mom fell in parking lot at home 2 weeks before WDW trip. She spends the whole trip in casts and a wheel chair.
Then there was January 2004 when my Mother tripped and fell walking along the deck in back of WL. She broke her wrist.
I guess you can see my Mom is a klutz. None of it was ever Disneys fault. She just can't be trusted to walk by herself. I'm not kidding.
Then last year in November my cousins and I went to WDW for the F&WF. We were having a great time till cousin Ed had too much to drink and took off. It took us hours to find him. He didn't cause trouble or anything, it was just irritating.