in a public place and like done your business and then reach for the toilet roll to find that there is none there.
some times you can get away with it, but i was in the gym and didnt really want to, and i had noticed that there was someone else in the changing room from the shuffling about outside so i cleared my throat and said "hello?" to which a voice replied with "hello?!" and i was like "oh ive just realised there no loo roll in here, can you pass me some please?" and she did.
it was a wee by the way. not a poo.