The most fair thing to do, oddly, is to leave the seat in the opposite position it was when you got there; everybody flips it once, it may be before or after you use it. Fair.
I'll remember this one, I love it when people are actually logical about things.
Reminds me of canal locks. The etiquette is to always close the doors after you leave, and people get angry when you don't. But it's infuriating because it actually creates more work for everyone. If you leave the doors closed then the next person always has to stop their boat to open them, but if you leave them open there's a 50% chance the correct set of doors is open for the next person to sail right in. If you're in the unlucky 50% it makes no difference, because you had to stop to empty the lock anyway and afterwards you get to sail off without closing them.
People also think closing them saves water, which is another can of people-not-understanding-physics worms.
I always think it's unfair to compare things to video games. Video games are so inefficient they had to invent a separate processor with hundreds of cores just to run them. Of course they end up running well.
If cheap phones had a 128-core JavaScript Processing Unit, websites would probably run fast too.