Class trick my mum played on my dad after they were first married - my dad has never been able to pay her back for it.
Dad was out the front washing the car on the communal car park. The hosepipe he was using came through the kitchen window and connected to the cold tap, which was on full blast obviously in order to create enough pressure.
Mum was doing a degree at the time and supposed to be revising for her exams at the kitchen table. Instead, she decided she was bored and wanted to annoy my dad. Creeping just out of sight to the kitchen tap, she very slowly turned the tap down and eventually off. Dad kept looking at the window but couldn't see mum who was ducking out of sight.
My dad, being a lovable eejit, then looked down the hosepipe. My mum, seeing her chance, turned the tap on full blast again dousing my dad from head to foot in freezing cold water.
When he came in a few seconds later, mum was curled on the floor in hysterics. Apparently she couldn't speak coherently for quite some time as every time she tried to she'd begin crying with laughter.
He's never forgiven her or got her back, and she's never forgotten.
