Ignoring the obvious crashing into the ground and everyone been killed scenario, I have personally been on a few flights which would qualify for nightmare status.
In each case the FA hated their job, and had no problems telling you that fact. So:
Candidate 1 - AA MIA-LAX in Y. No IFE, it was on a rather squishy 757, the FAs probably scolded half the pax, they got upset with me because I was buying a can of coke and a cookie with cash, this was still in the days that cash was accepted.
Candidate 2 - BA ORD-LHR in Y. At least there was OK IFE, however the flight attendant looking after our section again did not want to be there. Thanks to AA stuffing up the check-in (I was connecting from an AA flight), I was put into something like 53F, right at the back of the 747, in one of the final rows of 4 and in the very middle of the row of 4. The most memorable moment was when the FA forgot to ask our row if we'd like tea / coffee with breakfast. When we call her back and said she'd forgotten she stormed off in a huff because she then had to actually do work. (That amongst other things).
I've also had a few where there have been unpleasant pax for whatever reason, but nothing YouTube worthy.