At school, one classroom had a white board with marker pens rather than a traditional blackboard (this was a long time ago, in 1975). There was a weekly roster as to who was responsible for ensuring the water bottle dispenser was kept topped up, which was then squirted onto the wiper thing so the board could be cleaned.
One day, I saw the bottle was empty and even though it wasn't my turn to fill up the water bottle, I headed off to the toilets to fill it up, and on the way, the boy whose turn it was, spotted me, and said he'd do it instead, so I threw it maybe 5 feet to him.
This was seen by one of the teachers, Mr Cousins, who didn't believe I'd volunteered to fill it myself, despite the other lad confirming my story, and said I was lying when I said I had decided to fill it myself, and that I was merely playing around with the bottle, so the bastard gave me a detention.
I complained to the Head, and he agreed with Mr Cousins, even though I'd pointed out the inconsistency, that if I had genuinely been playing around with the bottle, why wasn't the other boy given a detention, as I'd thrown the bottle to him.
I didn't bother volunteering or helping out any more after that (changed schools as well, but that's another story).