One ride of CofP, at the ending scene, the teenage girl's hand was suspended with no sweater up to the wrist. The hand was exposed and appeared as if just hanging there. I'm sure there were parts I don't understand, but instead of her pale mauve sweater up to the wrist, it had slipped down and the moving hand was exposed. Very creepy. Once also saw the guy animatron talking at CofP, I think John? and his neck was slipping out of costume, and some mechanical details were exposed at the base of his neck where the shirt was supposed to start. Another creepola moment, but not as bad as the hand.
I've seen lots of boo-boos, mostly with various animatrons being still/out at the wrong times on Splash and PotC.
Also have ridden through a lot of dark rides with lights on, esp. TTA inside a lit up Space Mountain...walls are uglier than I ever would have thought.
Finally, a WDW cast member was a former student of mine who tripped and fell once and I spotted her in a video (she was a princess at the time).