When you really need a poo when everyone in the house is sleeping, and after defecating you don't dare flush the toilet in fear of waking everyone up.
"Hey, wtf man; flush it in the morning"
"Sorry dude, it was a banging night poo"
When you're dehydrated and drink a large glass of water before bed, your insides churn and suddenly you're up at 1am taking a giant dump.
Dammit, I didn't get any sleep last night! Drank all that water right before bed, and woke up an hour later to take a giant night poo.