It seems that asking your dad to put the toilet seat down is just not always enough — sometimes you just have to take matters into your own hands.
That's what an ingenious girl did after likely one too many times falling in the seat because of her father's absentminded habit. As the dad said on an Imgur post: "Apparently I was not doing a very good job remembering to put the seat down so my daughter made a warning system for herself."
The clever hack includes marking the backside of the movable seat "danger" and the backside of the lid "safe." It's clearly a helpful tool for the child, but maybe her dad will give it a second glance and do the right thing.
Because just remembering to do it on your own as a grown man is not enough. (No, we're not bitter.)