Because women always need the seat down, and men sometimes need the seat down. One study determined that 66% of the uses of the toilet in a mixed household required the seat to be down. Hence, putting the seat down is being considerate to the maximum number of people, regardless of gender. Because men already have to handle a bacteria-laden toilet sit to flip it up, they have to wash up with that in mind. Nothing about that changes if they handle it twice. But leaving it up means women have to handle it, too. Since nothing about female toilet habits requires handling the seat, it’s inconsiderate to force such uncleanliness upon them. So it’s not just considerate for women, to leave the urine-splattered rim covered at all times, but for men as well. However, since seat-up inconveniences women more than men, the refusal to do it in a mixed household is seen as an act of selfishness. The man in question would rather make the females in his house handle a dirty toilet seat, and occasionally sit in his urine splatter by accident, than just reach out and flip the damn thing down when he’s done.
Some folks are saying to to place the vehicle in park and then engage the handbrake as a way of “double braking” and keeping your ride in the same spot that you left it. This is fine, there is nothing wrong with doing it this way and as someone pointed out this is how the manual says to do it. The second answer people are giving is in regards to relieving the vehicle weight from the parking pin or pawl. Most of you that have parked your car on an incline or decline will notice that your shifter knob inside your car requires more muscle to move and make a clunking sound when taking it out of park. That’s because at an incline or decline(basically the nose of your car is pointed up higher than normal) the car naturally wants to start rolling backwards. The only thing that keeps that from happening is the parking pin/pawl located inside your transmission. It keeps the transmission gears from turning thus preventing the tires from rolling. It is possible if enough weight is placed on that pin, it would shear it off and the car would start rolling backwards in park. You can also shear your pin by placing the car in park while still rolling(I’ve done this one myself. So, the goal with the parking brake is to help out your transmission by taking the load off the parking pin. You do this by engaging the handbrake/parking brake which is not part of the transmission and doesn’t work by using the single point of failure like a pin. Instead it uses your rear brake and basically keeps your rear rotors or drums pinched preventing movement. So this is how it’s done. Once you’ve come to a stop on a slope or incline, keeping your foot on the brake pedal, engage your parking or hand brake fully. If your hand brake is functioning properly you can take your foot off the brake and even while not in park, the car will not roll. After the parking brake is engaged take your foot off the brake pedal, this allows the directional mass of the car to rest on the parking brake, then place your vehicle in park. Now none of the weight of the car is resting on your little parking pin. When it’s time to go, place your foot on the brake pedal, put the car in gear and then release the parking brake. The transfer of vehicle weight to the transmission is seamless, take your foot off the brake and away you go!