When you go take a shit, and the poo drops out from your bum and lands hard in the toilet bowl, sending a splash of water onto your bum, cleaning your bum so you don't have to wipe it with toilet paper.
Oh, WATER SHIT! The water that other people's shit have been in is now on my bum! Now I need to get a towel to... oh SHIT! Now where can I get a towel?