Class 700 units are particularly susceptible to severely overflowing toilets, but unfortunately there is no automatic CIS announcement for "flooding onboard the train"...
I did once end up involved in organising a stock swap to deal with a 377 which had a toilet on the brink of overflowing, and got the delay announcement set to "due to predicted flooding"...
I have also come across several trains delayed recently because the driver has somehow taken the wrong unit out of the yard. It is impossible to fully explain this to the public without sounding completely incompetent!
Perhaps the best excuses are best reserved for trains which leave early.
I remember an evening "contra-peak" service which had to wait at one station for 7 minutes for random timetabling reasons. Said train was rarely populated by more than 2 or 3 passengers. However, most of those passengers were known to misbehave. One evening, a ticketless gentleman harassed several other passengers and myself because he wanted a free taxi from "the railway", on the grounds that the Beeching Cuts had closed the connecting branch line which he wanted to use. (Bear in mind this happened in the last couple of years, so a fair amount of time had elapsed since the closure...!)
Unfortunately we had no choice but to kick him out, lock up the doors early and depart slightly before due time, as he was constantly trying to board the train and causing a general nuisance whenever he saw a member of train crew on the platform.
Fortunately, nobody else had much sympathy, and it took him most of the next three hours to get to the next station up the line, where he was last seen trying to get money, taxis or free train rides out of people.